I use a mix of Black Rapid shoulder strap and Canon E1 Wrist strap. I should note that the E1 only really works well with a larger camera body with a grip attached.
What I find the wrist strap allows is when you have the camera in hand at rest beside your leg. It lets you relax your fingers a bit and rest the camera on the strap. You can't fully relax the hand, but you can relax it a good amount. I find it pairs really well with the Black Rapid strap as that also lets you shift weight to your shoulder instead of purely on the hand - great for heavier lenses where the wrist strap then helps control the camera and lens swaying.
Note one trick I found with the Black Rapid is to not mount the camera directly to it. Instead I use an Arca Swiss quick release plate on the bottom of the camera and then you can get a small quick release mount for the Arca Swiss. This mount has a simple quick release setup on top to attach to the quick release plate (either screw or lever arch attachment); and then you can screw the black rapid to that. I actually glued mine in because I'll never unscrew it from that mounting.
This way I gain all the benefits of the Black Rapid, and if I want to take it off I just unscrew the quick release holder and away it goes and the camera is off. With the glue on the screwthread of the attachment point it also means its all the more secure.
It's a versatile setup that can do what I want when I want. If I want off the Black Rapid its seconds to get off and on; I can rest my shoulder if I want or have additional freedom or swap cameras or whatever. It isn't cheap, but Arca Swiss (or kirk) quick release plates are fantastic, the unique lipped design means that they never suffer rotation issues that manfrotto and others can suffer from.
