How often should I backcomb my dreadlocks? - Dreadlocks FAQ's
In short you never want to use backcombing to maintain or tighten your dreads. Backcombing essentially re-starts the dreads. Re-Backcombing takes any locking progress you have and resets it back to just knots. These fresh knots have to begin tightening again. In some cases, like when you have no decent knots in a particular dread it can actually be the best course of action since fresh knots will tighten and mature much faster than un-knotted hair. Check out this post about evaluating loose dreads that may need to be re-backcombed.