When are you going to use "much less than" when comparing?

Answer 1

Two examples:

I enjoyed that concert much less than I enjoyed last year's.

There is a large amount of sand in the little girl's sandbox, but it has much less than is in the big sandbox in the park.

Answer 2

The sandbox sentence is grammatically awkward, with ambiguous antecedents and confusion between the sand and the box.
IMHO.