The trigger fires the selected weapon group, which is usually the primary weapon (HBK-4H AC20 for example), while the "launch" button fires Weapon Group (X), where X equals a dynamic weapon group based on the mech and weapon load-out, so it's different based on both mech and load-out selection. If there are more than 2 weapon groups to choose from based on my weapon group selection, the weapon group highlight option is pretty quick as access the the hat is convenient. So, for example, the primary weapon for my HBK-4H is the AC20, the secondary weapon group consists of 4 small lasers, and weapon group X is a TAG for easy access. So, I switch between weapon group one and two via the weapon group highlight function based on the situation, while the launch button fires the TAG laser, regardless of the primary weapon selection.