There is NO Family Tree Maker App for the iPad. That is an Ancestry APP of the iPad. It accesses your Ancestry Member Tree (AMT).
I do all of my file maintenance from within Family Tree Maker for many reasons. BUT, I do have an AMT so that I always have my tree with me. Either on my iPad or my Smart Phone. I can also do updates from my iPad, as you do, but when I get back home, I do the SyncNow and any updates from my iPad, is now on my PC.
I was away for 5 days, but always had my tree with me.
There are many things I can do in my file on my PC that I can't do in my AMT, but that is only because I have been using the Family Tree Maker program for a long time.
Charts, Reports, Books, are things I can do from my PC that are not as easy, for me, from my AMT.