I know this is the worst thing to say on LHCF and I've never admitted it....but I blow dry my hair AND flat iron every five to six days. I know..I know...I've been doing it for years and actually I have no problems with my hair.
I don't know my hair type, its maybe 3a 3b, not relaxed, curly and I straighten it when i want to wear straight styles which is pretty much all during the winter/fall. Maybe that's why it hasn't affected my hair, b/c as soon as it gets hot I just wear it curly. I use a heat protectant before I flat iron as well. I just like my hair as straight as I can get it. Rollersetting dosen't work well for me b/c my hair is so curly, the roots don't get straight and I look like a big curly frizzy mess or if I do get it somewhat straight it reverts back to its curl in like 2 days or immediately after coming in contact with any moisture, humidtiy, whatever. I've practiced and it just dosen't work well for me.
I have an IONIC blowdryer, curling iron and flatiron. It works for me, I think it just depends on your hair type and how you take care of your hair. I deep condition, do hot oil treatments and during the warm months, I CW every day.