If you put the Whoopie Hook on the whoopie sling, you can use the whoopie for multiple hammocks. Putting the whoopie hook on the continuous loop makes it kind of permanent; i.e., non-transferable. I'm sure Dutch won't object if you buy a set of Whoopie hooks for each hammock!
This is the primary reason I leave them on my few sets of whoopies. Otherwise, I don't see a major with it, either.