IF you heat up your penis it will increase blood flow thats all. Were your ligs are located I think their is blood around it so I think the ligs are already warm from the blood. I gain without warming up and with Girth also but maybe thats just me.
I always warm up properly for both length - and girthwork. I also got a mild case of thrombosis a few months back from neglecting to do so. The thing is though, I only need like one minute to warm up and warm down, since I have one of those hand shower thingies attached to the wall next to the sink. I just hang my cock over the edge of the sink and shower it with high pressured hot water . It is much quicker this way than if I were to use a washcloth or heating pad, and the heat really goes deep into the tissues, since you're getting a water massage at the same time.