At the start of a match, it may be wise to give yourself a margin of safety for the first few games. This means selecting safe targets to get your teeth into the match, feeling your legs beneath you to find the rhythm of the ball, and assessing your opponent's abilities to understand what might be most effective.
After those first couple games, once you've got a good sweat going and calibrated your strokes to the conditions of the court (because every match the conditions will be change), there's no reason you can't open up and take more risks.
If you can start smacking winners from the first shot of the match like Roger Federer, then do it. But most players can't and there's nothing wrong with easing yourself in. Just don't mistake playing with a margin of safety with playing passive, conservative, or timid.
All it means is don't aim for the lines!