I use the hank on jib, because I do not have a furling jib. I use the halyard to tighten the jib as tight as I can, hoping to get better upwind pointing ability. I think the handbook says to keep the rigging a little loose, I just like mine tighter.
I usually sail solo and have my hands full, so I can't slack the halyard while underway. I use the main sheet to snug it up more for upwind sailing.