Microlearning works well for skill drills, compliance refreshers, and just-in-time job aids. It is less effective as the primary modality for content that requires sustained synthesis (literature, mathematics proofs, multi-step engineering problems) — those benefit from longer, structured deep-work sessions.
The strongest evidence base comes from spaced repetition research (Ebbinghaus forgetting curve, SuperMemo, Anki) — microlearning units are most effective when scheduled to repeat just before the learner is predicted to forget them.