Let me refine my first statement about weightlifting to failure.

I didn't mean every session. Lifting to failure at key times or even a 80%-20% type situation (except one tends to go hard in the gym more than 20% of the time) has immense benefits in building muscle strength and power/forcing adaptation. To make the big gains one should go heavy and to failure as a normal part of the overall training plan.

I fully understand the 80/20 +/- rule in cycling - I do 10/15 min intervals, 3-6 min intervals, long sessions of Z3 - but spend the majority of my time in Z2 or less. Probably too much time in Z2.

I guess the root of my question - can going to complete failure every so often, with a solid recovery plan in place, trigger some adaptations that one wont get without pushing that hard?