As mentioned, yes.

I have 3 second power, average power, normalized power, speed, heart rate, and power zone all showing at the same time (you can get up to ten pieces of data shown at once on Garmins). For specific efforts, I have another screen that shows me the all of the above for just that specific effort.

I also have a screen that shows me how much time I've spent in each particular zone (most useful for ensuring I'm not soft-pedaling or coasting too much).

After the fact doesn't matter very much for training. For training, what your'e doing and how long you're doing it is most important. After the fact is useful for when you're racing or doing a group ride or simply going flat out without concern for power. Then you can see the numbers and see what was good or what can be improved. Then you use workouts based on those numbers during your ride to improve said numbers.

It's a real game changer, but only if you actually utilize it. Using power like you would use speed, just glancing down periodically to see what you're doing, is pretty pointless. I look at my power meter every 3-5 seconds when doing a workout, and probably every 15-20 seconds even when just riding around, even though I've been using one for nearly a decade and have my intensities fairly dialed in. It's extremely stochastic when you first try it, but you can improve your ability to hold tighter power ranges with practice, and in my experience, the higher the power, the easier it is to hold steady (except for <30 sec efforts which are just hold on and die slowly).