How are different forcefields developed/evaluated? The Rosetta software can use a variety of different energy functions:

Ref2015
GenPot
Beta-Nov16

How are these energy functions developed and validated? Is it common to do a single protein design with several of these energy functions?
Some force-fields rely solely on theoretical physical principles, while others are tweaked specifically for the goal of accurately depicting certain structures like sheets and helices or movement/diffusion aspects at different theoretical temperatures of a set of well-studied proteins. (Top-Down vs. Bottom-Up)
I haven't done MD myself but I am in an MD group and people seem to normally stick to a single force-field for a given MD project but it happens that they do very short simulation runs with force-fields just as a test.
They definitely don't plan on doing the full simulation on different force-fields unless the comparison of those is their main goal.