We use it to send out client forms that require a signature. Its much better than sending it in an email because it can all be dealt with online without needing to print, sign and scan back a paper document.
Our forms are more professional looking and neater, if this was not easy to use it wouldn't be worth the time but almost any fillable form is either tied to this program or easy to download and complete.
I use pdfFiller to quickly complete forms. It even has my signature saved so I can sign the document at the end. Since I type much faster than I write, I prefer pdfFiller rather than printing and filling out forms my hand.