This is actually more complicated than it may seem. When you are smoking, a couple of things are going on. Moisture is a byproduct of combustion, so as you're puffing away, you're actually humidifying the tobacco in the lower part of the bowl. Further, there are other distillates that will develop from volatile oils and so on that will also accumulate. Then, when you let the pipe sit, oxidation takes place, and some of these components change dramatically. So, when you re-light, you're smoking something quite different from what you left the night before. Some people love this, others don't. Some call it the "Delayed Gratification Technique (DGT)."
The flavors the second day will be much stronger, but they'll also tend to be more acrid, and possibly bitter, depending on the blend. I find that Latakia and orientals don't tolerate this very well, but virginias are more forgiving.
In any case, moisture content seems to be a personal preference. It definitely changes the way a tobacco tastes, and, of course, the way it burns. I prefer my virginias a little moister than my latakia blends, because the additional moisture enhances the sweetness of the tobacco for me, while a somewhat drier latakia blend tastes smoother. I used to smoke my latakia blends almost bone dry, but after experimenting, found that changing my smoking style a little, and keeping the tobacco a little moister, provided more flavor, more depth, and less astringency. (Ironically, the reason I started smoking it dry was to avoid that astringency. I was just over-packing and over-puffing before.)
I've talked about the moisture content of tobaccos before, and you can find more information in my column,
Dust in the Wind, from a couple months back, as well as in
Tobacco Reanimation in the Briar & Leaf Chronicles.
Cheers,
Greg