Can be, but interface code is slow and flunky.
If you were creating some kind of search system, for example, it makes sense to leave the text in the box after searching.
I'm not sure if there's any secondary behavior to the "Don't use this control for commands" option, but it seems like an easy way for the BYOND staff to implement this would be:
-) Rename option to "Don't clear input on execution"
-) Don't disable the command box when it's selected
-) Always run a command if one is defined