basically it should be an option to allow the same grenade use than in arma 2. via the weapon fire cycle.

two main reason for it :

• to let people used with arma 2 controls to keep using the same ones.
• for realism :

in arma 3 the player is holding his rifle, and can magically pull the pin out of the grenade with only one hand.

in real life you can't handle a rifle and a hand grenade at the same time. you need your both hands to use a grenade.

putting the hand grenade into the weapon cycle would force you to switch weapon.