[jkaplowitz]

What if you're not sure if you want to trigger the effect of the button?

[e_proxus]

Unless I’m missing something we’re talking about a tab bar? The worst thing that can happen is that you switch to that tab. Switching tabs should never be destructive.

[chrismorgan]

Toolbar, not tab bar. You will regularly get mutating actions there, though any mutating actions should either prompt or be undoable.