Years ago, when my SO and I calculated our compatibility using OKCupid, there was a way to run a report on items that decreased compatibility. We didn't have many, but it was helpful to talk about the few things we did disagree on. I wonder if they were able to do something similar before their marriage; maybe it would have helped.
We didn't meet on a dating website, but my current partner and I have done pretty much this. We sat down, and talked, and had a very frank, logical discussion of the things we disagree on, to try and weed out any red-flag issues before they became issues. It transpired that politically, we're quite different - but we both think it's pretty boring to be with someone who feels the same as you on every issue, all the time. I think it was good to do that - to talk thoroughly through things in a calm way, before they turn up in a completely unrelated fight.