Some benefits (in no particular order) assuming we are speaking of the Ubuntu official repositories are:
- More uptodate packages. As of today, several months after the release of TexLive 2014 ubuntu 14.04 still has TexLive 2013 or PGF 2.10 in the official repos.
- More control over the system. Even if you only need the e.g.
tcolorbox ctan-package you have to find the ubuntu-package where they put it (assuming it's even packaged, see 3.) and install all of its content, which may be several megabytes of packages you'll never use.
- More packages. Sooner or later you'll stumble into a ctan-package that has not been packaged for Ubuntu. In such cases you need to perform a manual installation or hope for a third party/unofficial repository.
- Easier fallback in case something breaks. Say that the ubuntu packaging occurs while a broken version of a package as been uploaded to CTAN. If you're using ubuntu packages you are stuck with the broken version until the ubuntu-packager fixes its package, while with
tlmgr you'll get the fixed version as soon as it is uploaded to CTAN and can easily revert to a previous version of a single package.
I forgot my favorite: simplicity. Using Ubuntu packages you are basically introducing another layer of complexity over Texlive, since Texlive already is a distribution system that you are forcing into another distribution system (Ubuntu packaging). With more complexity comes less control, less understanding and a higher risk of breakage. Some distros (say ArchLinux) suggest to install vanilla Texlive over their own packages for the sake of simplicity.