It's always best to know where you're going before you leave!
Commonsense dictates one is better off being "ready" for marriage financially and emotionally in addition to making sure the marriage is solidified. There's no need to rush and put yourself under unnecessary stress.
The more stress there is in a marriage the more arguments there are which can lead to a decision to go your separate ways.
Decisions on will there be a stay at home parent or will you have enough money to pay for daycare indication to all the other expenses that come with having a family, doctor visits, food, clothing, car seats, additional insurance withheld from paychecks all the while you're trying to either complete an education, or pay back loans, save money to buy a home or establish a career.
Lastly there will be a large gap of time before it will be just the two of you after you start having children. Some couples never experience an empty nest as they end up raising their grandchildren. Enjoy your time as couple and especially having less responsibility and the ability to go places spontaneously without having to make baby sitter arrangements.
Few if any couples will say having children improved their romantic life, intimacy, or made their lives (less) stressful.