A LOT of information is posted in Global chat. Important information that the game gives you that you can only see in chat… You lose this and the ability to type commands when you switch to another tab. Maybe there’s a conversation going on in local, PMs, or guild chat you want to see but not global. (And speaking of counter, it would be really nice if there was a local cache because I actually do use it.)
Of course this will probably never be implemented seeing as multiple people have suggested this over the past 10 years without any tangible results, but who knows/cares seeing as I’m the first person to have posted about this in several years.