For over ten years now, there has been technology out there for playing electric guitar into virtual amps. These amplifier models were available in external hardware boxes at first, like the Line 6 Pod.
But now there are hundreds of modeled amps available in software form with programs like the Line 6 POD Farm. In fact, you can hear a cover of the song That Thing You Do! (from the movie) - along with the video of lots of versions of me playing guitars and bass all going through modeled amps - that I recorded using the Line 6 POD Farm in this post - Cover of “That Thing You Do” – Record a Rock Song on Your Computer.
These modeled virtual guitar amplifiers sound fantastic, and to a lot of people (heck, most people I would guess), they sound like the real thing. But still, there are detractors - people who say they sound fake. They prefer the sound of real guitar amps recorded with real microphones.
And let's face it, it is often preferable just to plug your guitar into your amp and shred. And if your band is playing live, you'll want to have the real amplifier - though it is getting more and more possible to play live with amp models using iPads and iPhones with products like the IK Multimedia iRig Amplitube.
I did a review of that product, along with audio samples, in my post AmpliTube iRig by IK Multimedia.
But if you are recording a rock song and only have one amplifier, it may be beneficial to enhance the sonic palette of your electric guitar sound by adding some virtual amps, or vice versa, blending the two types of sound for a more interesting and rich mix. Graham Cochrane did a recent video showing you some ways to do this. See that video below: