Why use iMic if I my Mac has Line-In? (Mac)
You certainly can use your built-in audio, but you may get better results with the iMic. The Mac's built-in audio hardware typically does not perform at professional quality levels, introducing noise and distortion. The inside of a computer is a very noisy place electrically; the power supplies are full of transient noise from the CPU, hard drives, CD drives and other computer components. The built-in Mac audio hardware can transfer that noise into the audio I/O (input/output). The iMic stays outside of your noisy computer system, attaching via the external USB interface. Normally this will provide improved performance for audio recording and playback.