Unless you're a bestselling writer, signings can be painful, and not because of writers' cramp. I've done standing-room only signings where the bookstore events person really knew her stuff, others where the only attendees were there by accident.
Book sales on the spot were never the real goal of these signings. Getting the store's salespeople to handsell it was much more important, and for that you have to shmooze and persuade them to read. Getting local media coverage was also a major goal.
But these days most books are sold online or through non-bookstore outlets like Target and Walmart; which means signings are even less efficacious than in the past.