Subversion doesn't distinguish between filesystem space and “branch” space; branches and tags are ordinary directories within the filesystem. This is probably the single biggest mental hurdle a CVS user will need to climb. Read all about it in Chapter 4, Branching and Merging.
Since Subversion treats branches and tags as ordinary
directories, always remember to check out the
of your project, and not the project itself
you make the mistake of checking out the project itself,
you'll wind up with a working copy that contains a copy of
your project for every branch and tag you
 That is, providing you don't run out of disk space before your checkout finishes.