Steve,
The reason not to do it is there is no reason to do it in the first place. IF the heads suffer from seat recession , then by all means have exhaust seats installed. If they do not , you don't have a problem to fix in the first place. Replacement seats have been known to "fall out" if installed with "too little" press fit , and crack the head under the seat if installed with "too much" press fit. Much paranoia was created in '72 when Ford cast a bunch of "junk" 351C 2V heads that had seat recession and horrible guide wear. As I mentioned gas formulations have been improved to reduce seat recession and it rarely happens now days.
Randy