Yes. Unless you are pecking at your keyboard your eyes are free to look at the results on the screen and stop typing once you get the result you want. The only thing that's needed is for the results to be stable, i.e. if the top result for "abc" also matches "abcd" then it should also be the top result for "abcd". Unfortunately many search/autocomplete implementations fail at this but that's still a problem even with "debouncing".
It doesn't matter how fast you can read the results, you benefit from instant results as long as you can read them faster than you can complete typing.
Whatever delay you add before showing results doesn't get hidden by the display and user's reading latency, it adds to it.
"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.
