What is the difference between putting logic in an event handler and putting it in an Effect?

Direct answer

Event handlers run because a specific interaction occurred, while Effects run because rendered state must synchronize with an external system.

Question	Event handler	Effect
Why does it run?	A particular interaction happened	Synchronization is required after rendering
Typical example	Submit order after button click	Connect to a room while roomId is active
Reactive?	No; runs only for the interaction	Yes; re-synchronizes when dependencies change
Common mistake	Putting synchronization here that should follow rendered state	Putting interaction-specific actions here

If sending a POST request should happen because the user clicked Submit, keep it in the submit handler. If a connection should exist whenever a particular roomId is rendered, an Effect expresses that synchronization.