For pickup trucks on snow/ice, the conventional wisdom is to throw some weight in the back (sand or cat litter) to add weight on the rear axle, increasing friction and making it less likely to go into a spin as the rear tries to go faster than the front. (And, should you have no traction, the sand or cat litter is right there to help).
On sand, you really don't need to worry about going into a full-blown spin without really trying - there would still be a lot of lateral drag on the rear tires even if they shimmy a bit. My experience in sand is that you generally need way more throttle than you might think as you try to push through the sand, and your problem is too slow and just bogging down. More weight results in more sinking into the sand, needing more throttle. Then you need so much torque to get going again that you just spin wheels and sink in further.
This can be alleviated to some extent by lowering tire pressures, increasing the tread area on the sand. Again, generally, you can't lower pressures enough for the sand to become slippery before they pop off rims (even with bead locks), and you continue to need more throttle than on pavement.
Now, my experience is mainly dry sands/dusts of the American southwest. Watching way too many videos from Australia seems to indicate that beaches, although damper or wetter, really aren't that different.