I sure don't believe that living together for however long is going to prove your compatability. You will face many different challenges throughout life that you have no understanding about until they arrive. It will reveal things about yourself & spouse you didn't know.
So maybe for some it helps give insight into that current phase of life but most folks with kids will tell you that life totally changes once you have kids, or when someone goes through hell at work, or has a family member pass, or become depressed or turn 30, or 40, or 50, or whatever.
The most joyous times of my marriage to this point (26 years in) were our early years. Hardly any adjustment it was all good. Her toothpaste habits didn't start bugging me until the rest of life ramped up. 4 kids, financial intensity, tough work life, getting older etc. I've had to grow up more in the last few years than ever before and I'm still working on it.
I guess we didn't need living together because we did a good job of being real with one another from the start. I wouldn't mess with a relationship in any other manner. I'm very direct with those I'm invested in. But I get that some do it differently.
As an aside, I am getting a bit of a kick out of those who insist living together helps prove compatability even when the stats say otherwise.