apex:actionfunction vs apex:actionpoller?

actionFunction : provides support for invoking controller action methods directly from JavaScript code using an AJAXrequest.Used when we need to perform similar action on various events. Even though you can use it in place of action Support as well where only event is related to only one control.

ActionPoller : A timer that sends an AJAX update request to the server according to a time interval that you specify. The update request can then result in a full or partial page update. You should avoid using this component with enhanced lists.Used when we want to perform an action on server again and again for a particular time interval.