Having the friends list exist as a separate window is something that i liked in previous versions of the Blizzard Launcher vs the current version with the new layout. Not so much for the separation, but rather, because it allowed the ability to move the friends list out of the way, when it got in the way.
This is not meant to be a complaint, as it isnt really a big deal (Its just the Game Launcher after all…). But rather to make the case for consideration to give us the ability to collapse, pop-out, resize or reposition the friends list in the future. As it would allow the user to better customize the Launcher in a manner that is more meaningful to them and cater to their individual gaming preferences and PC setups.