When composing a message, the attachment list is always visible. That wasn't the case in earlier versions (upgraded from 0.8.4). It feels a bit narrow with so much stuff around which I don't need. It's enough if the attachment list is shown when the tool button is clicked.
Also, is there a way to hide the contacts panel on the left side? Wait, wasn't the attachments list at the left side before? Maybe the two lists could be combined in one so that they don't take so much space.
I definitely agree with this.
Just upgraded a few days ago and I was quite surprised to see these big columns on either side of the compose panel, with no option to hide them away.
It would be good to have them only on request via a button as proposed, or to be able to customize this in the settings (had a look but didn't find any related option).
But thanks however for the great job you're achieving with Roundcube as a whole ;)