I used it a lot with my 300XL, especially for holds, where I could set OBS (called Hold on the 300XL), dial in the hold course, and then have a magenta line to track on my 396 (which was hard-wired to the 300XL and got its flight plan from it; the 396 has been replaced with an Aera 660). But with the GTNs and the GNC 355 that’s getting installed now, having the Hold feature pretty much replaces that.
There are times I lead formation flights and I like to set the airport as the destination, set Hold, and dial in the runway heading, again to give a nice magenta line to keep track of. I’ll probably still do that, if only out of habit, but with the built-in procedure turn capability, you’re right: there’s not a lot of times it’s used.
Add: I could also see it being useful to manage “Fly heading 030 to intercept V17, then direct ACT”; I could set it to ACT and dial in 001 and have a magenta line to watch.