Back in my infantry days, we weren't wearing any sort of PPE. It would have been nice, back then.
Having said that, fast forward to now and I have done a lot of pistol and carbine training courses.
Here is my opinion:
What you are doing (and where you are doing it) will influence the need for pads.
If you are doing a carbine course, you had better get some knee protection. Sure, you'll probably
be on a range with some nice soft turf (or fairly benign gravel). However, imagine yourself kneeling down
upon an upturned expended brass casing. Good pads will protect you from that nasty owie.
Alta pads are a decent pad, but they don't last too long. The Arc'teryx 'Military Knee Cap' pads are my
'go to' pads for knee protection. They last a long time and provide excellent fit, comfort, and protection.