Jeff, are you doing 2 bundle or 3? With 3 you can usually get away without reverse twists.
Does it matter, I don't think so. It is more asthetics than anything. I know of folks who will build without, and burnish it with a piece of leather, before seving. I think it is more of an issue, to not have too many twists in the body of the string, when finished!
Also, don't forget that the size or number of strands, can determine how many twists are needed in the reverse. If you only say do 14 strand strings and then go to a say 8 strand, ratio changes!
I can actually put the serving on a string, before building, and not put the reverse in and still have a rounded area in the serving. Equipment change!