The user intent is usually to get to what they are looking for as quickly as possible. If you intentionally introduce delays by forcing them to enter the complete query or pause to receive intermediate results then you are slowing that down.
> The user intent is usually to get to what they are looking for as quickly as possible.
Yes, and returning 30,000 results matching the "a" they just typed is not going to do that. "Getting the desired result fastest" probably requires somewhere between 2 and 10 characters, context-dependent.
