An important and common exception would be for performance critical reasons, as mentioned elsewhere. Say most of your code's in Python, but you rewrote parts in

An important and common exception would be for performance critical reasons, as mentioned elsewhere. Say most of your code's in Python, but you rewrote parts in a faster language. There you're not necessaryily separating them for isolation or encapsulation purposes. It'd be as much of a mistake to force them to hit separate DBs.