The title says it all, I suppose. I think at this point every mainstream editor and IDE opens the last opened project folder by default. This might be whole better to include this as a setting instead of an untoggle-able feature. Then allow closing folder/project if the setting is toggled on so as to switch to a different project folder. When the developer thinks of switching to different project folder every time he/she opens Builder is way too much of hassle, the settings itself can then just be disabled.
What do you think of this feature for GNOME Builder?