One of the big benefits of FTM is that you have control of your data. With the data on your computer what ever happens to Ancestry, you have the data.
There are other smaller features like telling you when you make an obvious mistake. I was just on an Ancestry tree where the parents were born 30 years after the daughter was born. While anyone can make an entry mistake, it is nice to have the program to at least warn you so when you post it online you don't look so foolish.