EZ Mix allows for some extremely quick effects and mix settings that can enhance your listening experience during writing. I find it hard to not fixate on less than polished sounds. Before using EZ mix I would find myself spending way too much upfront time producing, often times killing my inspiration. EZ mix may not always provide the final sound (sometimes it does, though), but it always provides a decent sound at the drop of a hat, keeping my focus on writing. For me this has become an essential piece of software.
Some of the presets are great, some are unusable. I'm specifically not a fan of the guitar tones which just sound too extreme no matter what adjustments you make. On the other hand, the vocal pack and mastering packs are very usable and useful. it's also expensive to get more than a few add on packs so it's best to wait for a sale or special event.