In tower defense there is a cool down to whenever you can send troops, the exp bar tells you when the troops are able to be sent. Problem is if you switch hot bar slots the exp bar goes back to full, and you won't know, which should be fixed so that it shows it no matter which item you decide to hold. In addition to this I think there should be a chat notification as to when you can send troops as well, for the purpose of convenience because nobody wants to stare at the exp bar, now do they? And in the case that a player thinks of the chat notification as spam there should be an option to disable it.
