Whats slippery for the stone is also slippery for the feet so there may be little net gain, except that rivers might be easier to cross if they were frozen over.

Oxen might have an advantage in the winter because then have a much higher ground pressure and might sink deep enough into the snow to get a good grip. If the stone was on a wide-based sledge its ground pressure could be quite low. 40 tons on a 40 ft x 10 ft flat-bottomed sledge is less than 1.5 lbs/sq in. That of a human is around 2lbs/sq in and an oxen is probably in excess of 6lbs/sq in.

I wonder if Neolithic crampons have ever been discovered and mis-categorised. They might have had flint points set into wooden soles.
;o)