The default behaviour of Jenkins is to empty a workspace and start all over, when the workingcopy is locked. In most cases an svn cleanup could solve the lock.

I'm working on a project where we have a 5.4 GB working copy, and our repo is litterally on the other side of the world. In such a case you don't want to do a new checkout (taking at least 2 hours), when "svn cleanup" would have been sufficient.