I think one thing that can help anyone is to understand how certain life choices would play out in the event of a split. A prenuptial agreement can certainly help, particularly if there's an imbalance of assets or earnings/pensions entering the relationship. Same is true if there are children from a previous marriage, as already noted. I insisted on a prenup for my second (current) marriage, as I had kids' interests to protect, and I was not interested in splitting my wealth in half a second time.
But perhaps equally important is understanding how your shared wealth and future earnings would be split in the event of a divorce. In almost all cases, unless it is spelled out otherwise in a prenup*, anything acquired during marriage will be split equally, regardless of who "earned" it. So if you're comfortable with the idea that everything acquired during the marriage should be evenly split, you have no worries. If you anticipate being a high earner compared to your spouse, or inheriting, or having a pension, etc., then you need to think carefully before commingling finances.
As an example, understand the ramifications of having one parent stay home to raise children while another is employed. There is no distinction in who "earned" the money and all the assets -- both parties contributed equally to the family in the eyes of the law, and it will all be split -- assets, earnings, pensions. The employed spouse could end up continuing to support that arrangement for life through alimony payments. Imagine, you have adult children who left home long ago, and you're continuing to support an ex spouse who doesn't work, and sits at home, for the rest of his/her life on your continued earnings (you still have to go to work), because that is the arrangement you set up 20 years ago when you were still married with babies! Oh, and your spouse left you? Doesn't matter, you still pay. There will be no early retirement for you, because your alimony payment will never be reduced, and certainly not by you choosing to retire early.
* Even with a prenup, you may be unlikely to keep things separate. As soon as an asset or earnings are commingled in any way, it's now marital property to be split equally. And a prenup likely will not be upheld if there's a gross imbalance.