Evolution RTS had /grabinput by default (via widget) and it caused me some ire.
Example of bad grabinput:
1) Anarchid starts an Evo game in borderless windowed mode.
2) While it loads, Anarchid goes from Spring-occupied virtual desktop #4 "Water" to Firefox-occupied virtual desktop #2 "Fire" and reads article about robot suicide.
3) Spring completes load.
4) Grabinput takes force.
5) Invisible window on hidden virtual desktop prevents all input to system. Good luck if you know how to quit spring blindly.