Yeah, I also use that all the time. I use the terminal because I want to use my keyboard, not the mouse. And copy / pasting is something I do very very often. So I don't understand why people make a terminal multiplexer and don't add this feature.
In screen & tmux you can also use vim shortcuts to navigate the scrollback buffer. That is so convenient and makes me work so fast. I can search for a snippet close to where I want to copy some text, and then navigate more precisely with the vim shortcuts.
So that's the first thing I look for in a terminal multiplexer, because if you're gonna expect that I'm gonna put my right hand off the keyboard and use the MOUSE to awkwardly select some text in a TERMINAL, then you expected wrong.