Must admit that I haven't made them that way. Seems like extra work to make and tie in the second loop. May be an old world way of making a string.
Rolling the string on the leg keeps the two bundles separate, which I don't think makes for the best string. By making the first loop in the standard way, then back twisting the strands before making the second loop, all of the strands form one smooth bundle when you twist them later. This is a stronger construction I think, i.e., one cable of 14 strands vs two cables of 7 strands wound around each other. I could be wrong.
Regardless, no doubt that either construction method is sufficient.