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A carbureted engine, for the purposes of comparison:

A carburetor can only deliver fuel if there is a pressure difference
(vacuum) between its venturis and the ambient air. No difference, no
fuel flow. Throttle plates and chokes are there to provide vacuum for
the venturis, where the fuel outlets are.

Also, the carb is located far from the valve head, with long, cold
manifold runners in between. A large amount of fuel condenses on the
manifold walls and on combustion chamber walls when cold, so you need
lots of fuel to ensure that enough reaches the combustion chamber to
start the car.

The only way of ensuring extra fuel with a carburetor is to provide lots
of suction, hence the use of a choke plate.

A big downside of all that vacuum is that it's harder for the starter to
turn the engine over, and at just the time when you need the most
cranking effort.

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A port-fuel injected engine, on the other hand:

Is fed with pressurized fuel, so vacuum is not needed. There is less
condensation on manifold walls since the injectors are located just an
inch or so above the valve head.

However, combustion will still be somewhat inefficient until the engine
warms up, since fuel still wants to condense on the combustion chamber
walls, so extra fuel is still needed on startup. Since the computer
finely controls fuel flow, it can precisely mix the air and fuel for
better starting, unlike a carb which _must_ feed a very rich mixture.

This means the engine's controls are set up to feed extra fuel AND air
on a cold start. Correct mixture (rather than overly rich) means faster
cold starting and lower cold emissions.

Finally, the absence of a choke plate and the presence of the auxiliary
air inputs greatly reduces pumping losses, so it's much easier for the
starter to turn the engine.

Most auxiliary air is supplied by the IAC, which opens extra wide on a
cold start.