This AWeber review covers why AWeber’s autoresponder service is the one that many top marketers use and this review also discusses the advantages and disadvantages of using AWeber:

Tracking analysis features with AWeber are far superior to any other autoresponder that have the same features but at a far higher cost than AWeber.

Plus, if you’re just starting out with your email newsletter, AWeber can pro-rate your fees according to how many subscribers you have. This means you pay less at first, and more as you grow your list. This is a rather cost-effective and money-conscious effort on their end, in my opinion.

Small businesses are NOT taking full advantage of their customer contacts and leaving a lot of money on the table because of this..
Small business owners are also not following up with their customers in such a way as to retain their loyalty.

A customer list that is easily contacted by email is a gold mine for small businesses, and even more so for larger businesses, therefore an autoresponder is necessary for business, and the AWeber autoresponder service has been known as the prime service for years now