I'm not sure I understand the point of using an expander after a compressor as one reduces the dynamic range but the other increases it again. What about a little eq cut/boost instead?

There are all sorts of reasons to use an expander after compression/limiting:

https://www.gearslutz.com/board/so-much-gear-so-little-time/...

Sorry I still don't get it. That thread explains some uses for expanders, just not after compressor or limiters in the same effects chain. Surely if you need an expander after a compressor then you've got your setting wrong on the compressor, or maybe you need a noise gate before it.