Going hard often and training to failure may create adaptations but it will also weaken and compromise your immune system. You'll be getting sick more often. Then there is a possibility of CNS burnout too.

In 60 years of training, never happened to me. Too many hours per week of high end aerobic work would do that though. I only trained aerobically to failure once a week, if that, like 60+ miles hard enough to make it really hard to walk when I got off the bike. That plus training to 1 rep from failure in the gym every week worked like a charm. The best thing about staying one rep from failure is that one doesn't need a spot, that is if one knows what one is doing. I think one's results from doing that are just the same as failing that last rep. That said, there's no good reason to train to near failure until one is in good enough shape to handle it. One should wish for a wheelbarrow when leaving the gym. Do that consistently, long enough, and you'll wind up training to failure or near failure. It'll just happen. If you're not getting that tired, you aren't getting the results you could.

The above assumes that you know enough about nutrition to avoid just getting weaker the harder you work. If you use it up, you gotta put it back.

I used the morning resting and standing-resting HR method to watch for overdoing it aerobically. Found that to be the most reliable method.

I did power lifting 25+ years ago - we did failure and 1RM on many movements.

If you think about it, the entire goal in power lifting is to get 1# less than your complete failure weight off the ground. And in essence, doing your 1RM is exercising to failure - because you cant do it again.

Huh? You aren't going to failure on a 1RM unless you fail. Plus, no one really maxes out in their training, at least, no one who's doing it properly. Hitting a true 1RM outside of competition is rare. You're testing, not training when you do that.
It's been about 10 years for me, so maybe there is new stuff out there, but I can't think of a single powerlifting program that advocates training to failure.

Sheiko - nope
5x5 - nope
5/3/1 - nope
Smolov - nope
Starting Strength - nope
Westside - nope (while maxing out is done regularly, it is never a true max, there's always a few lbs left in the tank, and you certainly aren't intending to keep increasing the weight until you fail).
RTS - nope

You'd have to be a fool to think that failing with 100s of lbs on your back is a good thing. Not to mention how much doing this on heavy compound exercises, particularly lower body exercises, takes out of you. Failing does happen occasionally, but no one is deliberately trying to make this happen.

Now, going to failure on some assistance exercises, particularly ones that are isolation exercises, is pretty common. I will agree with that.

Without calling anyone a fool - AI will explain what I'm saying for me (and its essentially what I just said, highlighted in bold)

-Weight training to failure involves performing an exercise until you can no longer complete another repetition with proper form. This technique, also known as muscular failure, is a popular strategy in bodybuilding and strength training to maximize muscle growth and strength gains. While it can be an effective method, it's not essential for everyone and may not be suitable for beginners.

Here's a more detailed explanation:
What is Training to Failure?

• Not Just About Lifting Heavy:
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  You can reach failure with lighter weights and higher repetitions, or heavier weights and fewer repetitions.

• No Reps in Reserve (RIR):
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  It implies completing a set with no reps remaining in the tank or no reps in reserve.

• Momentary Muscular Failure:
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  Training to failure means reaching the point where your muscles can no longer produce enough force to complete another repetition with proper form.

For what its worth - I power lifted for close to 12-15 years or so and had a natural, no lifting shirt, bench press in the 505-515 range. Clean, no drugs, competition acceptable lift's.
I lifted with strong man competitors that made me look like a piker.
We all trained at the same gym with the same methods.
And yes, we would often lift at or above our planned competition weight, especially with the bench press. And we did that using spotters.

I like lifting lighter weights for very high reps and volume. Even with light weights I never ever go to Momentary Muscular Failure, I've tried lifting to failure in the past and I find it to be counter-productive in the long run. Training to failure is basically programming your body, brain and neural system to fail. I make sure I achieve fatigue but i always leave few reaps in reserve. I don't really do intervals on my bike because I much prefer zone 2 rides, maybe once per month I will sprint a little bit but I never ever max out.

And even this is still extremely uncommon in powerlifting. So me one popular training plan that calls for this. Just one.
https://www.powerlifting.sport/filea..._Men_Final.pdf
In the world championships this year, there were 5 men, out of 18, in the superheavyweight class that benched 500, and they are no more likely to be "clean" than a top cyclist is. If you're going to tell stories, at least make them believable.
This leads to the obvious question: why would you do less than you're (apparently) capable of in competition? Unless you were doing some sort of massive cut, this doesn't make any sense.

World record raw bench press is 782#. I had guys in my small local gym (not clean mind you) that were in the 650++ club, one or two close to or above 700.

So in cycling terms, my 510+/- is similar to a bike rider having a 4.75wkg in a world of 7+wkg riders - not really that impressive.

I was born to bench press. Short arms, barrel chest, big triceps and as the lifters called it - bench pressers elbows. What ever that means. I could do dips at 225# body weight, with 3 45# plates hanging from a chain on my weight belt - 8+ reps for multiple sets. 120-140# dumbbell incline presses for reps - I was strong in the bench press, triceps exercises, shoulder presses - any pushing exercise. Everything else I was MEH, not so strong. Strong, but not at the same level as my bench.

my last statement makes perfect sense. We would intentionally lift beyond our max, attempt to push more than we could - and in essence, if we cant do it - that = failure. Training to failure - yep, we did it.

Believe what you want - call me a liar - I don't care. I could and did lift those kinds of weights and we did train to failure on purpose.