It's the only way that you can truly manage the effectiveness of how and what you're eating.
If you're consistently inconsistent then that's great! You're a raw canvas. You can basically start anywhere with a new nutrition behavior and focus on that one thing for 3-4 weeks and see some progress before adding something else. You might be someone who eats healthy during the week and then falls off track on the weekend. Or maybe you're someone who simply doesn't have any strategy when it comes to nutrition and some days you eat like a high-performing athlete and then the next day you eat like a teenager playing video games until 3AM with their friends.
If you're consistently eating poorly, then you're like someone who is consistently inconsistent. Mostly any healthy nutrition behavior modification will work.
The key is once you become consistent with your healthy eating behavior modifications, then you will want to stay consistent with them in order to see real progress.
For example, if you decide "I'm going to have breakfast everyday and it will be a protein based smoothie" then you want to stick to that habit 90% of the time to see any progress. Keep in mind, you may not see any progress at all as far as your body composition goes during that time, but that shouldn't deter you from keeping it as a habit. You will simply need to do more than you're currently doing and add to that habit.
Pick something that you're SUPER confident that you can successfully do 90% of the time. This will help get the ball rolling and build your confidence.
Do it consistently.
Then when you're ready, stack the next habit on top of that.
You would be amazed what adding 5-6 healthy habits over the span of a year can do for you mentally and physically.