Adding the PPA (repository) upgrades the existing desktop (1.12) to the new version (1.14). It's not separate, but if desired, you can undo this update by later removing the repository and then re-installing mate-desktop.
I don't know how much space it will take, but it could be up to 100 MB as it updates MATE's core apps too.
If you're low on space, take a look at Bleachbit (it's in the Software Boutique) which can reclaim disk space (in particular, apt's cached packages and unused localisations). 