Hi Yip,
It is much easier to inlet a lock if you remove as much wood off the sides as you can before inletting it. It is easy to determine how much wood to remove because you can measure the thickness of the lock bolster and then just leave 1/16" more wood. That way you don't have to bury your lock deep into the wood preventing you from seeing gaps and risking chipping out wood every time you remove the plate. So many folks seem to want to attach all their hardware first and then start trimming and shaping the stock. IMO, that is a huge mistake.
dave