I'm not sure if it does serve any useful purpose, though there's no harm in asking. Maybe someone who has disrobed will offer a personal perspective.
In simple terms, greed, hatred, and delusion are the reasons why monks disrobe. Of those monks I have known who disrobed, the number one cause was lust. Most got into a relationship with a woman.
However, that doesn't really answer the question very well. All monks who are not Non-returners still have lust, but they don't all disrobe — they find ways to overcome those feelings. There are other factors at play such as discontent that lead them to get involved with a woman in the first place.
Its a very personal decision, and knowing one monk's reasons is not likely to help someone else. If one asked instead, “Why did you get divorced?” one would get the same kind of answers. Desire for another woman, discontent with the current marriage, but would it help anyone contemplating getting married? It depends on so many different conditions that it is hard to predict what will happen in ten years from now.
Check out the community that you plan to ordain in, stay for an extended period before ordaining, then make your decision. Ten years spent as a monk may not help your career prospects, but its never a waste of time. You will definitely learn a lot about yourself that will benefit you later in life — things that you would probably never learn as a lay person. Think of it as doing a ten-year retreat instead of a 10-day retreat. Someone who disrobes in their thirties after ten years as a monk is more likely to ordain again at sixty-five than someone who has never ordained before.
• • • • (Upasampadā: 24th June, 1979)