Won't hide staves with fermatas
The thing is, if you have one staff with a fermata, every staff has a fermata that measure, even if they are in the middle of a 20 measure rest. MS3 refuses to hide these staves, so whenever I add a fermata, suddenly I am looking at every single instrument in the score, like I don't have 'hide empty staves' enabled at all.
This wastes all kinds of ink, and makes large scores unmanageable. 
Comments
This is a bug. Fermatas shouldn't prevent a staff from being hidden.
Edit: I double checked and it worked properly in version 2.3.2.
It appears I broke this a few years back (!) with a change designed to make sure text would make a staff be considered not empty. See #44956: Empty bars with text not visible when hiding empty staves. Open to suggestions as to which items that you can attach to rests should or should not be considered. Both text and fermatas are considered "annotations", and my code currently doesn't distinguish by type - only by whether it is a "system" element and whether it is visible.
Meanwhile, as a workaround, you can mark it invisible, but still have it visible in the part.
In reply to It appears I broke this a… by Marc Sabatella
I'm not so sure you broke it where you think you did, because it wasn't broken in 2.3.2 in my testing. Perhaps it only broke master (now known as 3.x) but didn't break 2.x, I'll let you figure that out.
Besides fermatas and caesurae I don't know what else should allow a staff to be hidden.
In reply to I'm not so sure you broke it… by mike320
I should have mentioned, I did verify my fix was merged only for master, I think because there was concern it would represent an incompatible change.
Looks like breaths/pauses are ignored, so we should be good there.