reports the position of t1 in list t2. (if you don't know what that means it means temporary1/2, used in scratch 1.4)
So if you have a project that deletes parts of lists, but it doesn't know where it is, it can't delete the specific one. With this you can do it!
This is possible with certain scripts, but isn't it easier just to have a block that does it for you?

Not sure I quite understand the feature, but it sounds like a good idea!