If I have learned something since starting developing and selling my own software
, then it is to never, never, ever, remove a feature when creating a new version of your software. No matter how stupid or irrelevant or buggy you think the feature you want to remove might be. Because there will be people who use this feature. And who will absolutely be pissed about you removing that thing they need.
I think this is also one thing which Microsoft didn't get, when they decided to remove the start menu in Windows 8, and replaced it with the fucked up start screen, which doesn't even contain half of the features of the start menu.
If you need to remove something, then don't remove it completely, but hide it instead, so that if users who rely on this feature can at least find it and continue using it.
On a related note: One similar important thing I learned as freelance developer is this: although it might be tempting as programmer to rewrite a whole, old app or parts of it completely because it is now absolutely fucked up and not maintainable anymore, don't do it, for the same reason. People rely on the strange and probably even buggy features deep inside of old software, and you can never reproduce all of them easily in a rewrite.