It depends. Do you mean circular wiggle where the crown goes clockwise and counter-clockwise (as when you are winding it up), or direct side-to-side wiggle? A little circular wiggle is normal for most watches. Direct side-to-side wiggle can be trouble. On mechanical movements there is a VERY tiny screw almost directly over the crown stem in the movement (on quartz models there is usually a depressable tab instead of a screw) that keeps the stem in place. Wiggle is a good indication that screw is starting to loosen. What follows after that is the crown and stem fall out.
If you're in doubt, just take it to the nearest watch repair shop for evaluation.