Tyler Cowen, writing for the New York Times.
When restaurants don't charge for reservations, they tend to hold back tables for regular customers, celebrities, very attractive people and the politically and socially well connected. You might be dying to go to that restaurant for a special birthday or anniversary, but you'll simply be unable to get in. Money is ultimately a more egalitarian force than privilege, as everyones greenbacks are worth the same.
This applies to far more than just restaurant reservations, of course. All scarce goods must be rationed. That rationing can be done by connections or cash. I'd prefer that it'd be done by cash, putting everyone on an even field of play. (Those without cash can earn it, raise it, or be given it. Connections are much harder to come by.)