Subversion allows our developers to checkpoint their work when they reach certain milestones.  For example, once they implement a feature, they can check in their code, to ensure that they are able to return to that point.  This is useful for several reasons.

1. A developer is able to revert, “check out”, back to a known good version of the source tree when needed.
2. A source control system enables our team of developers to share a common code base, and work together on applications.

We use a subversion server that is offsite, so in addition to the above benefits, we have an offsite backup of our source tree.  For security reasons, we don’t access the server through the subversion protocol, but we tunnel all requests over ssh. Each of our developers generates a ssh key pair, and we install the public key on the subversion server.

XCode has built-in integration with subversion. So, once the repository was checked out, it is very easy to set this up.

Here are some other pages (1, 2) that reference subversion and source control systems.