What if I don't change my Master Cylinder on a disc conversion?

Alright now. I didn't mean to cause a stir. I've read so much about brakes and bore and stroke in the past, I just wanted a little education. I was going to upgrade the MC anyway. Posting a picture of me in my swimsuit was a bit low, but does motivate me to lose weight. Seriously, though, thanks for all the posts and education.