I have searched and read some comments, but would like to hear current thinking.
I am going to order a 2017 f150...I like my iPhone navigation apps much better than the Sync 2 navigation on my 2015. Can I/should I just get Sync 3 without navigation? Any disadvantages?

 

Just ensure it has Carplay / Android Auto compatibility. Carplay only has Apple Maps as an option currently so that is the limiting factor. I haven't heard of any plans to allow Google Maps or Waze.

My 2017 I ordered came with navigation otherwise I wouldn't have added it.