I have done quite a lot of beach driving over the years including towing. Initially my D2 did not have CDL. As good as it was it was better again with CDL retrofitted. I always engage it on the beach, even hard sand, and drop tyre pressures. I would never wait until I'm in trouble and then lock. With the D2 bogging down and then deciding to lock the centre diff isn't going to be much help and if you are towing chances are you are well stuck and need to break out the shovel and drop the tyres down to silly levels just to get out and then have to pump them up (but not to road pressures) before moving on. Now throw in an incoming tide and holding up your mates and it's just not a good idea IMHO.
There is also more vehicle sympathy in having CDL locked in soft sand or hard sand where soft bits will be encountered versus the likely prospect of one wheel spinning like a top with CD open.
Cheers

