If your shower has stopped holding a steady temperature, or the handle has become stiff, that is usually the valve behind the wall rather than anything you can see.
You may not need to lose your tile
This is the part worth knowing. Many valve repairs can be done through the existing trim plate, or through a small opening in the wall of the room behind — often a closet. Before you agree to having tile taken out, it is completely reasonable to ask whether the valve can be reached from behind instead. Very often it can.
Older tile is hard to match
West Ashley bathrooms from the fifties and sixties often have tile that simply is not made any more. Working around it takes a little longer and is nearly always worth it.
Sudden temperature changes
If the shower runs cold when someone uses a tap elsewhere in the house, the valve has worn. Beyond being annoying, it is how people get scalded, so it is worth attending to.
A stain on the ceiling below
In a two-storey home that usually means the shower base, the drain connection or grout letting water past. They are three different repairs, and working out which one before opening anything is the difference between a small job and losing the bathroom.