In ZBrush (and other sculpting tools) holding Shift lets you smooth without having to change brushes, strength/radius settings etc.
In the landscape editing mode, there seems to be no reason why Shift couldn’t be given the same functionality (so far as I know Shift isn’t doing something else while in Painting mode).
Hi Tom,
By default the landscape tools are not bound to any key, but you can go into your hotkey bindings and make SHIFT go to smooth mode. This is located in Edit>Settings>Keyboard Shortcuts>Landscape Editor. You can then set up key bindings for every mode you want to quickly switch to. I hope this helps to resolve the issue.
Thank you,
Alexander