I'd agree that a heavy crew is useful to get to do things outside the cockpit like external checks. I prefer having three people up front for takeoff rather than the full complement as I find a conversation taking place that I'm not part of rather distracting.
I also prefer to have the heavy Captain sit with the passengers as 1 Captain & 2 FOs is easier to manage and more natural than 2 Captains & 1 FO, IMHO.
On occasions, having four pilots working flat out has saved the day, like on a long haul bad weather diversion with a medical emergency piled on top that I had some years ago. If there hadn't been so much capacity available we'd have never made it back to destination within the max. allowable discretion.