I will try to make this as less subjective: Till what point do you continue doing exercises at end of the chapter to learn something: I do it in Grad school and that's where I really learn. Do professors/post docs learning about new fields do it too?
Exercises fall at various levels in Bloom's Taxonomy. Exercises at the higher end of the taxonomy are harder to do, but verify more objectives, since they rely on understanding and applying knowledge from the lower levels.
To try and answer your question, I'll generalize a bit and say that academics are by nature quick learners for the lower-level objectives (knowledge, comprehension). Exercises at this level are probably less useful than Upper-level exercises (application, analysis, evaluation, creation).
However, whenever I haven't taught material in a while, re-doing some of the knowledge exercises is a great way to freshen up and be sharp for class.