Here is a top-mounted Kahler (not original to this guitar) that needed to be routed 3/16" into the body... for a couple of reasons:
This made it possible to set the action properly. The action could not be set to a playable height when the bridge was top mounted. In addition, the neck was glued in, so shimming it was not an option.
Routing also made it possible to achieve the proper down pressure on the saddles. Before the repair, the strings would flop on top of the saddles when they were lowered, killing the sound and sustain. The bridge rout was best for this guitar, and the customer was very happy with the results.