It's the tool for compressing the bottom bushes on the front dampers on all models so you can get the split pin in the correct, inner hole. It also does the same thing on the body end of the diff plate panhard rod.
Worth having, although on the front there are ways around it, which would probably be more difficult on the panhard rod. TBH it wouldn't be difficult to make one.
I've certainly given my one a lot of use, it make the job so easy.