Therapy is a commitment, and like all commitments it needs nurturing. Attending therapy at least once a week means that you can maintain the bond of trust between you and your therapist, and not lose sight of the train of thought or the rising emotions and memories you find yourself working on.
Having your sessions at the same day and time each week can also help you feel trust in the process. That time becomes yours to be yourself in. And even when life gets chaotic, therapy is something you can rely on.