I've wondered this as well, because it seems no one uses them anymore during loading or malfunction drills.
I fired an AR-15 for the first time this year since I was last issued one 22 years ago and I hit the forward assist just like I was trained after chambering the first round. The cadre from my first unit were Vietnam veterans who experienced reliability issues with the early versions of this weapon in country, and ordered us to always use the forward assist.
I was not impressed with my first issue rifle, because it felt cheap and came chambered in .22 caliber. I later came to embrace it, because of the accuracy of the platform.