At its most fundamental level evaluation is information collected to base a decision on (Hervey, 2000, p.67). This information can be of statistical and/or intuitive in nature. It is a dual process of monitoring patient progress and making judgments about the course of treatment. This process can be formative (on going) and/or summative (at the end).
Evaluation is used to guide and direct treatment; to ascertain the problems and needs of the client, program, and institution. Evaluations can be used to predict future behavior, to monitor change and to know when to stop treatment (Cruz, Berrol, 2004, p. 26).  Evaluations are often used to establish a baseline of the client, the program and or a particular behavior/movement pattern.
As an autistic person I am constantly evaluating people, places, and things. When I was a child I developed a process of evaluating my siblings footsteps (weight, gait, and speed), breathing (amount, speed), and postural / gestural expressions to determine the likelihood of being punched. it constantly worked quite well.