Q: One is called "Best fit "and the other is "Sort by Lengths" but how does this setting change the results of the optimization?
A: Best fit may generate a more efficient optimization, because it doesn't worry about the order of output. Sort by length will cut longer pieces first so shorter pieces can stack on top of the longer ones.
NOTE: There is a compromise that is being made. In the following examples, Sort by Length generated less waste and a lower TLF for offcuts, but the offcut lengths might not be as usable.
Sort by Length