From my personal experience, it is usually being boxed in and being forced to settle wherever possible, most often not very optimal. I would assume that has a lot to do with the 2nd settler the AI get. Given enough space to breathe, bit of practice, experience, and self control usually keep you away from breaking your economy. Many times you feel as though you have to break out by warring to give yourself some room, but that war can also destroy your economy and slip you further behind in tech as well.