I used to clarify once and sometimes twice a month, but now that I use way less products with cones, I only clarify when my hair has build up or when it feels like I need it.
This can now be once a month to once every 8 weeks. It all depends on which of my products I used the most in a given month. Even many of the leave-ins and daily moisturizers I use now do not have any cones in them.
I now purchase way less shampoo than I used to, no matter what type they are. I use far more conditioners and I purchase conditioners to shampoo in the ratio of like 10:1.
ETA:
I like to use gentler clarifyers like CON Clarifying Poo, Aubrey Organics Gren Tea Clarifying Poo, Elucence Clarifying Poo often but I also use Mizani Puriphyl, Mizani Phormula 7 after a relaxer and ORS Aloe Clarifying Poo after washing my hair in hard water and when my build-up seem a bit stubborn.