I'm guessing that you're referring to the fact that you often have to put a 'return false;' statement in your event handlers, i.e.
<a href="#" onclick="doSomeFunction(); return false;">...
The 'return false;' in this case stops the browser from jumping to the current location, as indicated by the href="#" - instead, only doSomeFunction() is executed. It's useful for when you want to add events to anchor tags, but don't want the browser jumping up and down to each anchor on each click
When and why to
Er ... how about in a boolean function to indicate 'not true'?
When using jQuery's
each function, returning true or false has meaning. See the doc
return false using only if you have some worng in function (by some test) or you want to stop some function, example use return false in end "onsubmit"