I don't like having to run the HPS for 24 hours, it gets hot. Also, the spectrum of light that it puts out isn't ideal for the veg stage of growth, it's too red (so to speak). It's just like the sun... in the late summer months the light that hits the Earth is more red at that time, and so plants have grown accustom to getting red light and starting their stretch and early flower phase. So now, even in hydro tents grown with artificial light, color spectrum plays a huge role in how a plant grows. The bottomline effect is, if you veg with HPS lights you generally cause your plants to stretch more than they would under whiter or bluer lights. CFLs come in all sorts of spectrums, HPS not so much. That's why a lot of growers use MH bulbs/ballasts for Veg and HPS for Flower. I'd rather use a MH bulb, but don't have a ballast and didn't think to get one of those dual-function ballasts when I bought my light, so I just use the CFLs.
Maybe in the future I'll spring for just one of those dual-function ballasts. That way I can use one tent to veg all the clones (if I switch to 2-liter SOG, I can fit 10-12 plants in one tent for VEG, then switch half of them over to the other tent use them both to flower), and while the other isn't being used, I can dry in it.