How many times did you do some change in some file thinking <<this is only temporal, I cannot do check-in to this file>>, and finally you did. With this tool you will can mark a file as "protected", avoiding unwanted check-ins!
How it works: once you install the extension, you need to enter in the tfs security settings and add a new checkin policy: Prevent check-in. From now on, you can mark a file as protected (right click on solution explorer -> prevent check-in). If you try to check this file in, you will reviece a error until you unprotect it