I find it very useful when doing CAD (with intent to 3D print something). It lets me quickly sketch rough shapes and note measurements I've taken, visualize ideas to show them to colleagues, do geometry "math" with less chance of messing up. Paper would work just fine, I guess, but RM has editing and undo, so reworking large regions doesn't result in attempts of striking out with more ambiguous lines.

So, to generalize, I'd suggest it for people that do bespoke construction of some sort often.