With more complex projects it is often useful to be able to specify multiple check-outs for a build.

For example, what we do at my work place is:

$ cvs co -r infrastructure_1_1 eng/infrastructure
$ cvs co eng/applications

But depending on what you're doing, you might also do:

$ cvs co -r infrastructure_newest eng/infrastructure
$ cvs co eng/applications

So it would be nice to be able to specify different branches for different check outs. You can't express this with a CVS module because modules can't mix and match branch specifications.