Well whether you have a big mixer or a small mixer, when you're making music there is all some kind of mixer involved whether it be in a computer, or on your desk or it IS your desk. A mixer takes all of your individual audio signals like drums, guitars and vocals and "mixes" them together so you can hear everything at once while still allowing you to make changes to each individual signal. Once the music is "mixed" together it makes it much more difficult to make changes to individual instruments. Some kind of mixing ability whether it be internal software or a hardware mixer is an absolute neccessity when creating music. Bigger "studio" mixers simply allow more signals to be mixed at once and allow more features like groups and have better signal routing options giving you more control. Generally big studio mixers are given more care and better parts when they are manufactured giving them better overall sound compared to budget mixers used in homes. Most noteably the mic pre-amplifiers built into the studio mixers will be of much higher quality and allow your audio to have a much better, more natural sound when recorded.
