What does the asset Ace Pilot from Rats day 3 do?
In the Rats mission, on day 3, there's an asset called "Ace Pilot" (which is a picture of a pilot smoking).
What happens once I buy it?
From the wiki:
Ace Pilot (Rats Day 3): This asset allows special Ace Pilot Bile to come and pick up the money closer to the bus. This helps players having to struggle their way back to the (Alex) chopper ensure the money quicker.