well i typed out a big post on how and why, but i accidentally hit backspace and deleted it all, and im not going to retype it all.

kid, if yu change geo after baking you're destroying your normalmap, it's rendered to work from your existing geo.
optimising is part of modelling process, doing it as a last step is plain retarded in every way you can look at it.

con, it's got to do with intersecting geometry pieces, if shit's so close together, the cage can intersect the wrong piece of geometry so to speak, and produce bake artifacts.