I like that it allows me to send documents from my computer without having to print them out first, which saves time! It's easy for people in different locations or with limited access to printers/computers to use as well because they don't need any special software installed (like other services).
There is nothing really bad about this program at all so far - but if you're looking into something similar then definitely give iFax a try. We are using iFax mainly internally within our own organization and we've been very happy thus far.