Creative hopelessness is an optional part of the ACT model; you don't have to do it with every client. However, if your client is high in experiential avoidance and only interested in feeling good or getting rid of her difficult thoughts and feelings, then you absolutely must do creative hopelessness.
Harris defines creative hopelessness as a conditionally mandatory intervention, obligatory precisely for clients most committed to experiential avoidance, and insists it must be delivered with compassion rather than judgment.
, ACT Made Simple: An Easy-To-Read Primer on Acceptance and Commitment Therapy, 2009thesis