"Click to switch folder" behavior is unexpected and annoying
When you click on a directory/folder inside a tree, Baobab automatically makes that folder the tree root and you can't see the whole tree anymore.
IIRC this used to be not the case in previous versions of Baobab and I personally find this behavior annoying for the following reason:
Typically when you single-click something in all GNOME apps, it just puts focus on that item, so the current behavior of changing the root node to the clicked item is unexpected.
I don't know about others, but personally I tend to click on folders to see their details in the right-side panel or just simply because I'm so used to the click-to-focus behavior in Nautilus that I do it without thinking. I think that similar to Nautilus, the action to switch the root folder should be bound to double-click, not single-click.
And while you're at it, could you please make the fold/unfold arrow button bigger? It's really hard to hit it and I end up clicking the folder instead of the button. Same for the up arrow button to back up one level.