As far as I know - no, it doesn't matter.
Whatever is in the included file gets put, byte for byte, where the INCLUDE "thisorthatfile.pbp" line is placed so you can have a source file wich includes two other files, which each includes two other files and so on. It's not a good idea to include the SAME file more than once though, if that's a "risk" you need to use conditionals to make sure it's only "compiled in" once even though it's included at several places.

Disclaimer: I haven't done anything like the above.

/Henrik.