You have probably heard that question before and it is one similar to “What would I do if win the lottery?” as they are both very vague and expect no actual answer other than “it depends”.
However, let us try to frame that question from the perspective of a couple that is aiming at becoming financially independent and who are willing to prepare for the most important expense of their life : their retirement years. If you can figure out how to get prepared for your retirement, you will probably find it easier planning for intermediate expenses along the way (houses, kids education, …).
In addition to retirement being the largest expense to plan for, in many developed countries, the pension system is broke. Our financial savvy couple has better have a plan to have enough money when the time to retire comes, especially if they are currently in their 20s or 30s: there will likely be no retirement or nothing meaningful to support your life-style.
So don’t count on it and start building your own retirement pot.