Unfortunately I cannot find the post where this was explained in detail, I think by @ZPV, but I can’t remember for sure. In any case, the gist as I recall, hopefully correctly, is twofold:What was the mechanics about aggressive AIs...?
Something about easier worker stealing, but other than that I don't know.
Edit: See WT’s post below.
2. When declaring peace, you get three times as much stuff from the AI as normal.
It’s entirely possible my memory is failing me on number one. But not on number two.
There are other consequences of aggressive AI, of course, such as more likely to declare war and so forth but I never paid much attention to those details.