By liking them, you're advertising them. Your "like" factors into your friends getting an update saying "jlarocco likes the Super Sandwich Stall", and thinking

By liking them, you're advertising them. Your "like" factors into your friends getting an update saying "jlarocco likes the Super Sandwich Stall", and thinking "huh, I should go and try that place". It's somewhat meaningless now, admittedly: I might not speak for everyone, but I've basically tuned out anyone "liking" anything on Facebook as white noise.