During aldol formation, I've learned that there is a second addition of water in many cases to cause a dehydration to occur that results in a double bond at the alpha and beta position to the carbonyl. Why does this specific reaction automatically dehydrate? Is it due to the benzene ring?
What do you mean by addition of 2nd molecule of water? Actually, that was not a clear statement. If you could show it in some of the mechanisms, it coul have been better to understand your doubt/question completely.
There is dehydration usually always associated with Aldol, if substrate has 2 or more (alpha) H atoms, even in absence of a Ph ring: in acid catalyzed as well as base catalyzed Aldols, though their mechanisms differ.
The reason is always a conjugated (with carbonyl) bond, which may be facilitated by a Ph ring, as in the given case.