Over past several months I've noticed that when our partners come here onsite. They like to build Windows Mobile images on their laptops while trying to get other work done at the same time. The problem with that is when compiler, linker, etc. do their job they slow down the computer significantly because there is a lot of compiling and disk I/O happening.
Interestingly Microsoft engineers that worked on the build process foreseen this problem. There is "secret" switch that is actually described in the documentation but not many people know about it. It runs all build processes in an idle priority. All you need to do is add "-m" to the blddemo command.
The pros of doing this you already know -- you can work without significant slowdowns while your image is building. The cons, however, are insignificant -- it might take 5 minutes longer to build the image.