Actually, a very good question, Jerry. If you fish around enough, you will find that it is very popular among the Japanese for them to rig with a big treble at the end of the jig when they are fishing for doggies. Now (please note - just my opinion) my view is that this is about the dumbest rig you can go with for doggies. Trying to get a hook to stick into the mouth of a doggie is one of the harder things to achieve in jigging in the first place. if you think you need to stick a hook hard into a GT, its nothing compared to a doggie.
Their rationale is a doggie attacks from the rear and you get a better hook up rate. I used to do this but I dropped so many fish and also, I hooked up on the bottom so many times!! You may get a better hookup rate but the retentiohn rate sucks!!
Even running single assist, I have had innunerable occasions where the hook has simply fallen out during the fight. A good friend of mine who is an excellent jigger hits the doggies so hard with his attempts to drive the hook home you have to see it to believe it. It helps being a big bloke too! When jigging for doggies, I'm now using the Fisherman Shidens which are a thinner guage and finer barb which in my view should (theoretically) be easier to drive home. I know a lot of experienced doggie jiggers who use two assist of equal or varying length. I have no doubt you get a better hookup and retention rate but at the back of my mind is also the thought that if the bugger gets away, I'd prefer him swimming around with one hook in it rather than two. That's why I only use one hook.
The other problem with running a treble off the back is that I think it increases significantly the likelihood of snagging up on the bottom. Not a worry if you're using Williamson jigs but if you're using Fisherman or Seven Seas jigs, it matters!!
As I wrote earlier, these are just my views based on my experience. Others may have the complete opposite view.
just curious. does anybody put treble hooks on the back end of the jig or do you go with assist hooks off the front end only and do you use 2 assist hooks or just one?