Several therapeutic approaches assign tasks between sessions, and clients often find this surprising. The rationale follows directly from the arithmetic of how little time therapy occupies.
An hour a week is a small fraction of a life
Whatever happens in a session competes with the remaining time, during which existing patterns continue operating undisturbed.
Approaches that expect change within that ratio have to find a way of extending their influence beyond the appointment.
Assigned tasks are that mechanism, converting therapy from something attended into something practised.
The relevant situations cannot be reproduced in the room
Many difficulties are specific to contexts a consulting room cannot contain: a particular workplace, a family gathering, a crowded shop, being alone at night.
Discussing those situations gives access to a recollection of them, which is systematically different from the situation itself.
Tasks performed in the actual setting produce information neither party could have obtained otherwise, including what happens that neither expected.
Tasks are tests rather than exercises
In cognitive and behavioural approaches, an assignment usually has the structure of a prediction followed by a check: what is expected to happen, and what actually happens.
Framed this way, an unsuccessful task is not a failure, since a task that does not go as expected produces the most useful material.
This framing matters clinically, because clients who understand tasks as tests report them very differently from those who understand them as performance.
Completion is one of the more consistent predictors
Across studies of structured therapies, the extent to which clients engage with between-session work relates to how much they improve.
The relationship is not simple, since willingness to engage also reflects other things about the person and their circumstances.
It is consistent enough, though, that therapists are trained to treat non-completion as something to be examined rather than as a lapse to be noted and moved past.
Not every approach uses them
Psychodynamic and some humanistic therapies generally do not assign tasks, because their account of change locates it in what happens within the relationship.
Neither position is a compromise; they follow from different views of what maintains a difficulty and therefore what has to be altered.
Anyone unsure why they are being asked to do something between sessions is asking a reasonable question, and the answer should connect the task to the specific problem being worked on.