Assuming that we're talking about the JUGS Gun that has been sold for the last 8-9 years or so, no.
The "P" simply means that the gun is in "Peak" mode, and that once it registers a speed, it automatically stops broadcasting a radar beam. To reset the gun, you must press the trigger. Then the speed reading disappears, and a radar beam is once again produced.
The "C" means the gun is in "Continuous" mode. The only difference is that now the gun automatically resets itself after a certain amount of time (5 seconds, I believe). You don't have to press the trigger when the gun is in the "C" mode.
The main advantage to "P" is that you can conserve battery power when in the "P" mode by not pressing the trigger until right before a pitch (I almost always used the "P" mode, and would usually wait until the pitcher began his delivery, or close to it, back when I had my JUGS gun). You will typically drain the batteries faster when operating the gun in the "C" mode.
Where you point the gun does not vary. You are always trying to point it at the spot where the pitcher will release the ball (well, roughly, at least; you may have to experiment some to get the most accurate readings).