To get even more in, it could be that while holding the trigger you can enter a button combination, and an ability (whichever one you mapped to the combo) is used. This would allow for even more abilities to be accessable.
A way i've known this to be done, is to have several abilities setup in a combo (it was a maximum of three which you could setup in any order), of which then you can map the combo to a shortcut.
