Hickory is much stronger in tension than compression, so heat treating evens things out a bit and helps to reduce set. It's very similar to trapping the back in this effect. They both help to even this inequality. One by hardening the belly and also ups the poundage a bit, the other reduces thr amount of material contributing to the amount of tension and also drops a couple pounds of draw. Both will make for a lighter weight for poundage bow and both reduce the amount of set vs doing neither.
Personally I love heat treating and do it to almost every hickory and black locust now I make. Heat treat does great things with black locust.
Kyle