OBS is a fantastic service. As other comments have pointed out, you can build for other distributions as well, but as an openSUSE user, I use it for quite a bit.
Some of the packages I would otherwise compile locally but that don't need to be in the distribution itself, I simply compile on there, add my personal repository to my repository list and they will stay in sync with other build requirements etc. On top of that, this allows me to have them in the package manager proper, and I can easily build my packages for multiple openSUSE versions, usually current (13.1), Tumbleweed and Factory.
OBS also makes it really easy to fork packages to fix something and/or apply patches, and depending on what kind of changes one made, it also includes pull requests. That way you can fix or extend a piece of software via forking, and if it works and might be useful for everybody, you can send your changes to the maintainer, who can integrate it if they find them adequate. This makes it quite a bit easier and lowers the barriers of helping "upstream" with improving the whole distribution.
Some of the packages I would otherwise compile locally but that don't need to be in the distribution itself, I simply compile on there, add my personal repository to my repository list and they will stay in sync with other build requirements etc. On top of that, this allows me to have them in the package manager proper, and I can easily build my packages for multiple openSUSE versions, usually current (13.1), Tumbleweed and Factory.
OBS also makes it really easy to fork packages to fix something and/or apply patches, and depending on what kind of changes one made, it also includes pull requests. That way you can fix or extend a piece of software via forking, and if it works and might be useful for everybody, you can send your changes to the maintainer, who can integrate it if they find them adequate. This makes it quite a bit easier and lowers the barriers of helping "upstream" with improving the whole distribution.