It's pretty necessary to inform users when messages haven't sent though, especially when these little failure indicators are hidden in the channels themselves -

It's pretty necessary to inform users when messages haven't sent though, especially when these little failure indicators are hidden in the channels themselves - i.e you need to be looking at the message to know it failed. If I post a message in a channel and go back to work, I don't want to find out later when I check for replies that my message didn't actually send - I need a notification!