I go in waves on this...every couple of days for a few months and then every three days and sometimes every fourth day for a while and then back to every couple of days. It depends on how good my hair looks or how lazy I am.
I am doing every couple of days now because lately my hair has been looking terrible! I could never do every day because that is just too much time, effort and products. And every fourth day is when I have exausted all possible hair configurations...all down, half up in a barrette or clip, ponytail or messy bun. If there were more ways I knew how to fix my hair, I probably could get away with longer as my scalp doesn't get very dirty since I don't use heavy, waxy stylers anymore!