I don't see the value; I never have. I understand that the market maker is able to extract profit from the spread, but they keep that for themselves. The original buyer and seller don't gain anything they wouldn't have gained otherwise, and it seems likely that one or both of them lose out on a share of that spread-profit.
I don't even own stock, but I believe the "value" is as simple as a reduction in the price for the buyer, along with an increase in liquidity for the seller, along with a reduction of the spread for both (which should make it easier to budget and make predictions).
