An important difference between Subversion and many other version control systems is that like CVS, Subversion's mode of operation is nonlocking. That means that if two users have checked out working copies that contain the same file, nothing prohibits both of them from making changes to that file. For users of systems such as Visual SourceSafe, this may seem odd, as there is no way to ensure that the two users' changes to the file don't conflict with each other. In truth, this is by design.

In the vast majority of cases, the two users' changes don't conflict. Even if the two users change the same file, it's likely that they'll change separate parts of the file, and those disparate changes can easily be merged together later. In this kind of situation, allowing one user to lock the file would result in unneeded contention, with one user forced to wait until the other has completed his changes. Even worse is the situation in which the second user changes the file despite the fact that the file is locked. When the first user completes his change and unlocks the file, the second user is stuck merging the changes together manually, introducing an element of human error into something that the computer can handle far better.