You can spend valuable developer time on every part of a project. The bulk of time is normally spent on coding up .cs, .vb, .resx and .aspx files. However, you could potentially have the following happen if you do not include other files in source control:* lose work
In particular, you should make it as easy as possible to see who changed what and who deleted what and allow a simple rollback to previous versions of non-code files. Files you should put in source control include:* XSL files
Things you don't store are:* Video files eg. avi