I'm just wondering how is the best way to utilize HIIT into a plan. If I am spliting training say into phases: leanout/cutting/hardening/bulking...What are ways or I mean reasons I'd be doing so(adding HIIT)? In other words...at different goals, what is the benefit? Or do you keep it for leanout/cutting exclusively? I do hold onto muscle very easily, put on LBM easily... so any ideas as to where/how I would/should use it?
Thanks.

I personally belive HIIT should be saved for periods of removing bodyfat. I dont do it offseason much. I do advise women to add a session or two per week in the offseason.

Some rules I follow, dont do HIIT after a training session and dont do HIIT the same night you worked legs or the next day if you can help from it.

Do HIIT on off days in place of your weigh training session. Stagger LISS and HIIT back and forth for optimal fat loss.