The downside of staying well-hydrated is all that water has to go somewhere. Nothing like really hitting your stride, only to find that your teeth are starting to float!
Now, it seems like if you're going to drill holes in your shoes, the link I hope to have listed below, wouldn't apply. Seems like soggy feet would be a lot better than a citation for indecent exposure. But what about leather saddles? What about wearing socks? Bike shorts?
The link also includes an instructive photograph (rear view, thankfully), for the visually-oriented.