I wondered if you ment forward assist. The short answer is: constantly
I always thought a reciprocating charging handle on the left side would have been a better design as that would have eliminated the need for a forward assist and also much faster and simplier to operate. The location of the T-handle in the center/rear is awkward and requires taking a hand off the firing position of the weapon, takes more time to grab and operate than a conventional bolt handle on the left. For police, target shooting and other sporting uses it's really not necessary in my experience. Folks have been arguing about this forever but pushing that button is darn reassuring and a requirement.
I always thought a reciprocating charging handle on the left side would have been a better design as that would have eliminated the need for a forward assist and also much faster and simplier to operate. The location of the T-handle in the center/rear is awkward and requires taking a hand off the firing position of the weapon, takes more time to grab and operate than a conventional bolt handle on the left. For police, target shooting and other sporting uses it's really not necessary in my experience. Folks have been arguing about this forever but pushing that button is darn reassuring and a requirement.