Question: If marriage is just a label and a tax break (Also, is it even a tax break anymore? In Australia (NSW) I think that de facto couples have rights pretty much on par with married ones), why don't you just do it the moment you enter a relationship with someone?
If it's just a label, and the way you type is "just a label", then I can see you don't care for how people label you. Ergo you shouldn't care if they label you as married. And if it's more profitable for both parties concerned, I can see no negative (pre nup pending) for you.
Then again, if a proper marriage is a sacred bond between two people that lasts for life, and takes a lot of planning, forethought, commitment, trust, honesty, love and a big ol' fashioned celebration with family and friends, I guess I'm just talking out of my ass.