I love it! I write my own services for it all the time. You can assign global hotkeys to them as well which makes it crazy convenient to be able to select text, a file, etc and invoke some script you wrote on them.
There used to be – pre-LLM days – a "Summarize" service that "summarized" prose to a length of your choice by deleting sentences. I'm sure it was once someone's pride and joy.
It's one of those NeXTSTEP things that was copied over.
https://en.wikipedia.org/wiki/Services_menu