Bibs are more comfortable than shorts, due to the lack of a waistband. Depending on the bib, they may provide more compression. I also feel that they keep the chamois from moving more than shorts, which can help prevent chafing on long rides.
So quick update. I had ordered the regular Bibs in a 3xl and received them promptly but found the legs to be far to big. Also discovered at the same time that the deluxe is what I really wanted. Dan was awesome, and worked it all out. Received the Deluxe bibs yesterday in a 2xl and they fit great. Endured the much expected ridicule from my children and wore them on my ride this morning. Very comfortable and a great overall value. I would highly recommend Dan and love2Pedal. Currently I use a champion c9 (target) compression underlayer and a starter (walmart) shirt. I think my next andeavor will be to try a real jersey as the one thing I was lacking in the bibs is any kind of pocket.