Saving vig isn't the only puprose..
I have two outs (1 euro exchange, 1 us exchange) that are horrendously slow at realising a price move. With G&J, three times last week I played big into a line move in progress, and with the exchange (prices adjust rather than the line) I got out into a decent profit. Those three scalps would've paid for G&J three times over, or Don Best 1.5 times..
Obviously that might not happen every weekend, but between tons of NCAA games, a slate of NFL and 7 days of baseball, I think most could recoup the costs if they have the time to invest.