I imagine it is a preference thing. If you hived a package of bee's that may have been raised on larger cell's. Thus over the course of a few years you may want to continue to cycle out comb to get them to regress.
Yes, you want to continue to expand your TBH as the bee's build out. It will give them space for brood as well as space for honey. You will always be expanding the hive until the flow is over. Essentially, as long as they are building new comb, continue to monitor and expand. Once they stop building comb they are probably backfilling.