A share on a pool is nothing else than a winning-hash on the real network, just with a lower difficulty (usually 1, but with more efficient/faster hardware, pools tend to raise the difficulty).

On a diff-1 pool and a network-diff of currently ~3mio, the pool needs about 3mio shares on average to find a block,
if the pool changes its difficulty from 1 to 2, it only needs about 1.5mio of those diff-2 shares to find a block and each of those diff-2 shares would earn twice the reward of a diff-1 share, nothing changes, except for the bandwidth usage.