the real difference is, possibly a small loss in speed by having all done.
i do most of the bows in my shop this way unless someone specifically asks otherwise...
its not often that a loop will slip up or down but it can happen.. 1 nock can prevent this...
however i have seen many times when 1 nock has slipped because of pinch by the release jaws and the upward angle most people put on the release..
if a string loop breaks that has two nocks on the inside,, you can simply pull the loop materail off and know that you nock set has not moved
and you can finish your hunt shooting off the string.. there may be a small change in impact but close enough to keep hunting..