WebDAV locks can be used to prevent two clients that are modifying the same resource from either overwriting each others' changes (though that problem can also be solved by using ETags) or wasting time making changes that will conflict with another set of changes. In a multi-user calendar system, an interactive calendar client could lock an event while the user is editing the event, and unlock the event when the user finishes or cancels. Locks can also be used to prevent changes while data is being reorganized. For example, a calendar client might lock two calendar collections prior to moving a bunch of calendar resources from one to another.
Clients are responsible for requesting a lock timeout period that is appropriate to the use case. When the user explicitly decides to reserve a resource and prevent other changes, a long timeout might be appropriate, but in cases where the client automatically decides to lock the resource, the timeout should be short (and the client can always refresh the lock should it need to). A short lock timeout means that if the client is unable to remove the lock, the other calendar users aren't prevented from making changes.