Generally speaking users expect instantaneous feedback. It would feel super shitty if every time you hit enter there was lag until a server roundtrip posted the message.
Messages that the server saw earlier could easily be inserted partway up, right? We're talking about ~100ms most of the time; that's not going to cause you to miss messages.
Some chat service I use does this and it's confusing because I don't expect it. I check the last message to see if there's anything new, not necessarily the scrollback.
Basically, it triggers an annoying O(N) operation whenever it happens :)
> It would feel super shitty if every time you hit enter...
I and many people I know don't agree with this. Instant feedback is nice, but not required. Moreover, if we need to choose between (instant feedback) and (knowledge of server receipt of a message and knowledge of message ordering), we'll choose the latter every time. (I'm glaring at you, Google Hangouts.)
Having the chat server lie to you about the state of the world always feels far worse than a delay between the time you submit your message and the time it appears.
Maybe the best way to claim top lane shouldn't be the first person to type "top" and hit enter.
Even if the server corrected the order messages were received it'd feel shitty to not get your lane because someone has a faster roundtrip to the chat server.
1) The likely worst-case trip time to the chat server is 250ms. [0] It's true that that's ~2.5x slower than the typical minimum human reaction time, but it takes a fair bit longer than this to type "top<enter>". [1]
2) The case where the server displays one message ordering to one player and another message ordering to another player is strictly worse than the case where the server takes 250ms longer to display the same message ordering to all players. The first case creates confusion and arguments, as well as feelings of distrust directed towards the chat software. The second case might cause a vague sense of displeasure at the quarter-second delay.
> Maybe the best way to claim top lane shouldn't be the first person to type "top" and hit enter.
Agreed. Perhaps people could be civil when they play their games. :)
[0] In this case, RTT doesn't matter. Only the time required to get a packet from you to the server matters. I think that we can reasonably assume that the worst case RTT from anyone who's playing a vaguely-latency-sensitive online video game to anywhere else on the Internet is 500ms.
[1] Honestly, it might take half of this time for the pixel issued by a draw command to your graphics card to appear on screen. [2]