3-Why is this better than using a regular microphone plugged into my computer?

When you plug a mic into your computer, even a good quality mic, the sound from the mic must be processed by the computer's soundcard. This process includes the powering of the mic, amplifying the mics audio signal and converting the microphones analog audio stream to digital (this is done in the A/D converter). Most computer soundcards do a decent job of playing sounds - music, computer bleeps, etc, but the microphone components are generally an afterthought and not designed for high quality recording. Also, the inside of a computer is a very hostile environment for the tiny microphone level audio signals and it is very easy for these signals to pick up unwanted noise from other computer components. Moving all of this processing outside of the computer eliminates these issues.