The main purpose of a sump is to add water volume to the system. More water equals more opportunity to dilute the nasties. The secondary purpose of the sump is that it's a great place to hide heaters, skimmers, etc, and keep your main tank looking uncluttered. A refuge is just another smaller tank that macro algae can be grown to export nitrates.
I have neither with my 46g. They're nice, but if you don't mind hang-on-back equipment, and heaters stuck to your glass, they're not a necessity. I've been able to keep my tank water parameters pretty darn pristine without them, but with good weekly maintenance. (Plus... the room under a 46g bowfront for a sump is pretty useless - as I see you can tell from your signature line!)