Information
Why
Feedback
Confirm actions (e.g. a button that shrinks slightly when pressed).
Status display
Visualise progress (e.g. a circle that fills up when uploading).
Guidance
Steers attention to important elements or changes.
Delight
Can put a smile on the user's face, emphasise the brand personality and appeal to users emotionally.
Improved usability
Make interaction smoother and easier to understand.
Principles
Subtlety and practicality
They should support the main function, not distract from it or impair performance.
Speed
Microinteractions should be fast and not blocking.
Consistency
Similar elements should have similar microinteractions.