The two biggest things that make meal prepping a no-brainer:
1.) Healthy, nutritious food to hold onto your precious macros.
2.) Cost effective/Money saving.
Lets dive into number 1 first. Gains/body shape happen in two places. The gym and the kitchen.... simple as that. You could have a great workout routine and be pumping all sorts of heavy shit, but if your diet is not on track, you'll be unhappy with your progress/results. You ABSOLUTELY need to control your diet. Get that under control, and you'll see huge differences rather quickly. Bitches will be mirin (or dudes will be checking you out at the gym.. which women secretly love, but act like they hate. logic much?)
Meal prepping allows you to use any healthy ingredients you want, while making it easy to grab the meal and go. Time is precious now-a-days... family, work, school, ect.... all things likely to have us stray from eating healthy simply because we don't have the time. Prep a weeks food in 1 day, and you have no excuse to eat healthy.
The second and equally as important topic is that meal prepping is cost effective. In the past few years, fast-food has come a long way. There are much healthier options available that can easily fit into your daily macro intake. The problem is, you're paying double or triple what you would if you were to buy the ingredients fresh at the store and prepare the food yourself. It is incredibly easy to buy a weeks worth of food for much cheaper than eating out or buying snacks every single day, and it gives you peace of mind that the ingredients are fresh, and the person making them is fresh (and/or clean).
Beyond all this, it gets us in the kitchen, which I believe is one of the most satisfying things a human can do. Whether your a natural Gordon effin' Ramsey, or someone whose cooking experience equates to a bowl of cereal, it's beneficial to learn. It will help your diet in numerous ways, and add a hobby which will improve your quality of life and those around you.