> What difference would it make in case of a divorce? hint: None

Depends on the country and local laws, I'd wager. Regardless, it's probably a good idea especially before a marriage has happened, though lots of people rush into getting married nowadays.

> I don't see how people could decide to have a life together with that sort of difference.

The fact of the matter is that some things can reveal themselves later in the relationship and having joined finances too quickly is probably a mistake. The hard part is that you can't really gauge when you have the other person figured out, e.g. the whole "rose tinted glasses" period that may drag on long into the relationship.