It's almost impossible to know how a little bit of long grass or sand will affect your swing. About the only sure thing is that swinging hard to accomodate the terrain is a sure recipe for disaster. This is the exact opposite of most other golf games, where hazards will usually just impede your distance a little bit. That's not how it works here. Trying to make up for some sand by slamming the ball will likely move you forward about fifteen inches, if you make contact at all.
Rough grass works in pretty much the same way, though it's typically more forgiving.
Take an extra few seconds before hitting to be sure that you're making the right choice. Most of my meltdowns have started from a fairway bunker, so a little patience and prudence exhibited here can go a long way toward keeping your final score down. It's also during the short game that you'll be more apt to play with the shot setup options. Playing a controlled draw, fade, flop, or punch can be very useful during the right situations, but you'll gain more of a feel for the TrueSwing system if you try these shots using only the mouse. It's hard to explain exactly how to accomplish all of these simply by moving the mouse.