Thanks for the link
Running
update.bat is necessary if you:
a) built a specific source tree for the first time
b) made any modifications to XRCs, icons, images or whatever other "meta" files
c) want to use the stripped binaries from the "output" directory
If you use the binaries from the "devel" directory (as I always do), you can skip
update.bat in most cases. However, it never hurts to run it, and it only takes like 5 seconds, too