This will sound like a really dumb question, however.. I dont see the use or point of the adjustable trigger stop on the USP Tactical... can someone tell me the purpose and reasoning behind it so I can mess around with mine. Right now I left it at factory setting... thanks!

The OT is so that once the trigger breaks, movement of the trigger mechanism stops.  Any movement of the trigger after it breaks only serves to pull the gun off target.  That is why you want it to stop moving as soon as possible after the sear is tripped.  The way you usually set them up is to shoot it SA and adjust the stop in until it will not fire.  Then screw it in until it breaks, then screw it in another one-quarter to one-half turn.  Then double check in DA mode.  If it does not release in DA mode then adjust it until it does, than in another 1/4 to 1/2 turn.
Or, leave it alone because it is set properly from the factory.  Unless it gets out of adjustment there is no reason to muck with it.