For people who will not get divorced this is a good idea (as long as each has some slush money).

For people who will get divorced this is a bad idea.

For people who might go either way, if you come into the relationship with similar amounts of wealth and no kids, then this is a good idea as everything you make going forward is a result of your partnership, no longer just you yourself.

For people who might go either way and who come into a relationship with a wide disparity in wealth or existing kids it is more complex.