Question: When migrating from R2008, do you need to migrate to intermediate releases?
Yes and no. Consider the various factors: Autodesk Inventor is only supported and tested 3 releases back.
Other factors can increase the risk when:
Question: Do I need to set the "Prompt to save for migration" option on in Application Options dialog?
Only when you want to migrate all files immediately and want to have a dialog prompt you to save files.
If you do not need to migrate all files immediately, do not check this option in the Application options.
More information in here.
Question: Will my sheet metal bend tables survive when I migrate my parts from R2009 to releases R2014 and after?
Inventor 2009 introduced a new sheet metal style library ─Bend tables and K-factor unfold methods of pre-R2009 parts migrate transparently
You do not need to migrate the Flat Pattern to take advantage of new features such as editing flat pattern, cosmetic centerlines, bend order annotation etc.