With going from a explore based file management system to PDM, one of the biggest pain points we had was people not checking in files.
I found this online and it has really helped our team, we now have shortcuts set up for users so they can easily see what they have checked out.
We have users that have moved this shortcut to their task bar so that with one click it searches the entire vault and shows what files they have checked out. If your vault is too large to search at one time, you can adjust your search settings to only search certain folders to speed it up.
Hope this helps.