I don't find a need to cut it at all, unless the ends start splitting. My ends pretty much never split, only like 2 hairs within a few months so I just individually trim those. I often trim any knots that I see, maybe once or twice a week, which takes a bit longer because they are on the individual strands, but most of them are towards the ends. Detangling is probably the most important part to be careful & limit the amount of knots created.