Just to add to my video, plug-in automation can allow you be very creative musically and sonically. It also allows you to apply certain effects to a specific part in your music. For example, you want to create a telephone sounding vocal during the chorus and a different sound for the verse—plug-in automation can help you do that. This applies to not just EQ plug-ins, but Compressors and any other plug-in you can think of.
The significance of plug-in automation is that it can only be done in the box. In the outboard gear world, there is no automation. In order to achieve this in outboard gear, you must turn knobs on the fly while you are recording or printing. This can be time consuming and inaccurate.