The 1 advantage that i know of is that it reduces the latency of the signal from your guitar, so you can hear on time what you're playing as you record.

But besides that, what are the other advantages of using an audio interface instead of just plugging your guitar into the mic input of your pc?
Say you wanted to record with a certain amp tone that you have.

Also other guitars (i.e. classical and acoustic) don't have the capabilities of D.I. so they need a microphone to be recorded.
Let's see:

Multiple number and types of inputs/outputs (XLR, 1/4inch, MIDI, S/PDIF, RCA etc etc)

Pretty low noise floor compared to your run of the mill onboard soundcard. (that means less static and hum)

As you said, near zero latency.

Phantom power on some of them.

I've never looked back since I got my interface, granted it has been a pain in the ass (it's a Fast Track Pro and i've had lots and lots of problems with drivers and faults) but it has allowed me to up my recording quality dramatically.
Your music doesn't sound like balls **** ass shit

I don't have to tell you that your a retard for plugging your guitar into your mic port

You don't look like an idiot when you come on here wondering why your mic port no longer works because you were too stupid and overloaded it and blew your mic port

Free software

Do you need any more reasons?
Derpy Derp Derp Herp Derp
Two main reasons?

Preamps and A/D converters.

That is all you should need to learn about, to realise the difference in quality..
Hey, look. Sigs are back.