...in the middle game it can be difficult to figure out if you have several cultured cities (viz. culture > 10 or > 100) clustered together. It can be easy to exceed the Domination Limit in this situation.
For example: You're 1 under the DL....you abandon a city thinking you are "Re-claiming" 9 squares and build a new 9-square city somewhere else. BUT, you forgot that a city near the "old" city has say 150 culture points and thus the Borders were NOT actually reduced in such a way as to give you the 9 squares you thought you were getting!