It doesn't leak at night as pads do, it's cheap and environmentally friendly, but mainly that it doesn't dry out my mucus membranes and doesn't contain bleach and pesticides that I don't want anywhere near my uterus.
Hip hip hooray! May they improve all menstrual weeks for hundreds of years!
Congratulations on your 3 year anniversary! I recently started using a menstrual cup and the only thing that I'm sad about is that I didn't start with this sooner. It's amazingly great in every way!