There's no need for it at all, if the developers are really that desperate for it then they should make separate versions, one with micro-transactions one without but I remember people getting into arguments with me about this saying that if they did that then no one would play the free version and that's because micro-transactions suck . The thing is, when it comes to these things what you're essentially paying for is cheats this is why you don't see games developers putting them in anymore like they used to, they'd much rather you pay tons of money for them and now they've even had the balls to make you pay for tiny bits of content that would otherwise have ended up in a big expansion pack.

The only time I think you could truly get away with micro-transactions and such is if you were running something like Second Life to cover the costs of having stuff uploaded and things like that but there really has to be better way of doing this sort of thing.