Jeffro-
I think it will depend on your goals as to how you work cardio in, but let me share with you my moitivation for doing some form of cardio 6 days/week. I do HIIT (stationary cycling: 20 minutes, 5min warmup and cooldown, and 10 bouts of 30sec sprint/30sec baseline) after lifting during 15s and 10s- I don't have much left after 5s, so I don't do any cardio on those lifting days. Besides, given that I do drops during the 5s, one could argue that I'm doing HIIT then anyway. I do moderate cardio (NordicTrack skiing: 50 minutes) on my off days. I take one day of rest per week.
The motivation? HIIT keeps the subcu fat at bay and enhances my V02- good for situations like when the elevators at work break and I have to jog up 7 flgiths of steps
. The moderate cardio hits more of the visceral fat (often a problem in us old geezers, especially the guys), but also provides a sustained cardio workout to keep my endurance level fairly high (good for when I take 15-20 mile hikes with my wife and kids). It also provides documented benefit in keeping your lipid profile in good shape (there's not enough evidence yet to show that HIIT has a beneficial effect on HDL, which is why I don't rely on it as my sole means of cardio).
I've been using this schedule for a couple of years, and I've been very happy with my growth (which is still happening, BTW- even after almost 3 years on HST). Does this much cardio cut into my potential gains? Perhaps, but at 55, I have to trade off on gains vs. cardiovascular fitness (including V02 as well as lipid management).
Anyway, that's just my story- I know others in here have their own!
Jake