it's true, but they don't hurt either:
1. they help to jump start your account and make it seem more legit (people prefer following back accounts with a few hundred, thousands followers than if you have close to 0), these autofollowback people are a very convenient and easy way to make a follower base
2. there are advertising companies out there who pay after purely the number of followers you have (revtwt CPT ads, twtmob, spronsoredtweets)
3. if you want to sell your account/sell tweets, follower number is a big factor (not everybody knows that they're bot followers)
P.S. You don't even need followers on twitter to promote your offers!