Suchmaschinen sind was schönes (kann man nur empfehlen ;-):

With /INCLUDE, SQL doesn't expand the copy member, but instead just passes the /INCLUDE on to the compiler. The compiler sees the /INCLUDE and opens the copy member. So SQL doesn't see all the things in copy members that it doesn't like (like nested /copy and all the stuff that's supposed to be conditionally excluded).

You can use /INCLUDE everywhere you use /COPY; for both SQLRPGLE and RPGLE programs. /COPY is only required when the copy file contains things that SQL needs to see, like host variables or embedded SQL.