Microinteractions differ from features in both their size and scope. Features tend to be complex (multiuse case), time consuming, and cognitively engaging. Microinteractions on the other hand are simple, brief, and should be nearly effortless. A music player is a feature; adjusting the volume is a microinteraction inside that feature.
A definition of a micro-interaction in comparison with the bigger feature from:
Saffer, Dan. «Microinteractions». Beijing: O’Reilly, 2013.
The text further describes what microinteractions are good for:
• Accomplishing a single task
• Connecting devices together
• Interacting with a single piece of data, such as a stock price or the temperature
• Controlling an ongoing process, such as changing the TV channel
• Adjusting a setting
• Viewing or creating a small piece of content, like a status message
• Turning a feature or function on or off