I found this in the TortoiseSVN Book regarding using the Copy/Merge vs. Lock/Unlock
Here is a great article on how to merge VI's in subversion.
Subversion generally works best without locking, using the “Copy-Modify-Merge” methods described
earlier in Section 2.2.3, “The Copy-Modify-Merge Solution”. However there are a few instances when
you may need to implement some form of locking policy.
• You are using “unmergeable” files, for example, graphics files. If two people change the same file,
merging is not possible, so one of you will lose their changes.
• Your company has always used a locking revision control system in the past and there has been a
management decision that “locking is best”
