I later realized I could have squirted silicone caulk onto the holes in the tile to overflow into the air gap and so provided support for the grab bars. Some years later I installed grab bars with screws into the blocking and had to be careful not to screw in too tight.
I don't remember if shim stock was placed on the blocking so, between the studs, there was, or could have been, a slight gap between the backer and the blocking. Retiling a shower seals cracks and prevents water damage. Removing old tile costs 1.50 to 5 per square foot. But the blocking for grab bars was put in before the shims and was lined up with the studs. The cost to retile a shower is 7 to 25 per square foot or 800 to 3,000, depending on the tile type, layout, and shower size. The original drywall was removed up to where the tile stopped and shim stock was placed on the edges of the studs so that the outer surface of the new backer lined up with the 1/2" drywall above it. (It was certainly a pain to drill through.) In this job the tile used in the shower walls was left over porcelain floor tiles 18" x 18" so much stronger than standard bath wall tiles. I have seen one shower redo in which the original backer was 1/2" standard drywall, but the redo under the new tile was a single layer of cement backer board of thickness slightly less than 1/2".
A 42" long bar horizontal on the long wall is useful even for young and mobile users, and a 24" long bar horizontal on the end wall helps with ingress and egress of a tub shower. Maybe 2x4 blocking at shoulder height and 2x8 blocking centered at 36" above the floor for future installation of grab bars. If the tub or shower bottom is placed so that the wall must be single layer (green wallboard or cement board), it might be a good idea to put blocking between the studs.
What remodeling contractors often don’t tell you, though, is that the gorgeous tile you see splashed across Pinterest and remodeling magazines is very expensive. In any case it needs to be demoed and redone. Traditional showers with tile surrounds offer a lot of options in terms of aestheticsafter all, you have literally thousands of different types of tile to choose for your shower surround. Unless the person was huge and really slammed into the wall, this damage is evidence of a seriously substandard shower wall.