When are the metal legs under deck posts needed?

My old deck had the 1/2 inch high set of metal legs under two of its
three 4x4 wooden support posts.

But all of the posts stood on cinder blocks. Were the metal legs
really needed?

I thought they are to keep the termites and other living things from
getting from the ground into the wood, but doesn't the cinder block
fulfill the same function? In the case of one of my new legs, it
rests on a 3 foot by 3 foot cement (or concrete?) slab. Isn't that
good enough also, without the metal legs?