While the situation you describe is one that some people end up using it for - it's not the real reason mosh is useful.
Where mosh really shines is when your IP is changing too frequently (a mobile problem when you are on the move) and when you are dealing with high latency connections.
When you have to ssh in somewhere over a shitty, barely working mobile data connection - mosh is a lifesaver. It makes an otherwise unusable situation comfortable and productive.
Sure, it's handy for jumping between connections, on/off wifi and so on - but that's easy to achieve many other ways with tools that have been around for a decade or two at this point.
Yeah mosh is amazing. Just using screen isn't nearly as good because you still have restart the ssh connection. I usually have 5+ open at once so restarting them all is annoying.
Several commenters are asking what mosh provides that's better than ssh+screen/tmux.
A few years ago I spent a summer at a remote field site, sharing a flaky T1 with 100 other people over equally flaky site-wide wireless network. (Many of those people were undergraduates who had been politely asked not to use the research network to access facebook, but, well, you know.) Not only was packet loss common, but latencies to an outside host varied whimsically from 50ms to 2000ms. In those conditions ssh was unusable, tmux or not. I was able to do work on remote servers only because of mosh.
Mosh is absolutely fantastic. The reliability and recovery of the connection works even over extremely low bandwidth and lossy connections (e.g. when using a covert IPv4 channel), and instant local echo for responsiveness, as well.
Mosh is possibly the most useful piece of software that I've seen: it makes remote links over slow, unreliable networks bearable for doing Real Work. Speaking as somebody who usually has two rubbish networks between the computer I'm on, and the conputer I'm connecting to, that's incredibly useful.
mosh is fantastic for me when working remotely over vpn.
I don't have to worry about reconnections, disconnections, packet lag (due to local echo feature). mosh in combination with screen (or tmux) gives scrollback support + other features
Personally, I prefer to use irssi over mosh but other people (often your friends, colleagues) are more comfortable with a webUI. It's easier to get going since you set everything up for them and they only need a browser.
I've spent the past year using Mosh from high latency, unreliable satellite connections in Afghanistan. I would have been pulling my hair out without it. My only complaint is the scrollback buffer often gets jumbled.
Mosh support roaming and intermittent connectivity which is really super useful if you have to debug a server on a very dodgy 3g connection in a moving train.
I simply could not work without mosh. I do not experience significant lag and it allows me to have connections open even if I switch from WiFi over to 3G and back which is often the case.
Mosh is lovely, but keep in mind that you can't use agent forwarding, nor use it in pipes. On the other hand, if you're stuck on dodgy Wi-Fi or just about any mobile link, or you want to close your laptop and resume your session elsewhere, it's an absolute godsend.
Mosh backed up with either tmux or screen is handy indeed.
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