The "find" in the filter stage is intended to be used when you have a list of items (such as keywords) that exceed the visible display area in the Filter Stage. If the keyword (for example) you are looking for is not currently displayed, typing in the keyword should cause it to be displayed in the filter stage.
Note that if the keyword is already displayed, then you may not see any effects visually.
Hope this helps clarify its function.
Regards,
-Pablo