Comment by maxbond

"Instant," in the context of a user interface, is not zero seconds. It's more like 50ms to 1000ms (depending on the type of information being processed). If you want your user interface to feel snappy and responsive - then you don't want to process things as fast as the computer can, you want to process them in a way that feels instantaneous. If you get caught up processing every keystroke, the interface will feel sluggish.