If you've tried to bribe a city and had it rebel next turn, you've probably seen the hit you take with the Senate for losing it. If instead you give it to another Roman faction and they lose it, they take the rep hit. The problem here is that the AI will never turn down a gift, even if they have no chance of holding it, so for example the Julii will quite happily take a gift of Sidon, even though it's so far from their capital it's guaranteed to rebel.