Like others have said, there are MANY disadvantages- UIC or any other form of incontinence is an adverse medical condition, afterall- means something in our bodies is not working the way it should. So in addition to the host of management difficulties, diapers and everything that goes with them included, some people experience terrible medical side effects as well, or their incontinence leads to other conditions that could be worse.
But to the intriguing question about ADVANTAGES... one I can see is that one doesn't really have to ever worry about "finding" a bathroom, since you, metaphorically, are "wearing" your "bathroom." That could be an advantage on things like long flights, traffic jams, long lines, etc. I mean, eventually you have to change your diaper, but you can plan far ahead for that if you wear diapers that have long capacities.