In this post I don't want to convince you that you need to meditate. I want to explain what creating a habit of meditation can do for you, and you can decide for yourself whether it's something you value enough in order to give it a shot or not. If this post was titled "Why lift weights", I would be saying that lifting weights increases your strength and/or muscle mass, and will probably make your body look nicer. If that's something you want and value, obviously lifting weights is one way to go about it.
If you want to increase your capacity to exercise conscious control over the content of your own mind, or in other words to be more the influencer of your thoughts rather than to be influenced by them, you should practice meditation. Specifically, you should start with single pointed focus meditation.
How to perform single pointed focus meditation
Sit in a meditative position (ideally on a meditation pillow with your legs crossed, or on a chair with your feet touching the ground. Your hands resting on your knees or your lap. Your back straight but not stiff. Find a position that instills awareness in you but where your muscles aren't contracted). With your gaze forward, close your eyes or keep them partially closed (find out which is preferable for you by trying both. Some people experience disorienting distortions of space or even hallucinations with their eyes closed which can be an interesting experience but detracts from the purpose of this meditation. If you experience such distortions, try keeping your eyes only partially closed).
Take a few deep breaths, inhaling and exhaling through the nose, and scan your body for any stiffness. If you find a stiff muscle, relax it. Pay attention to facial muscles: Mouth, around the eyes, your ears. Return to normal breathing, still via the nose. Don't try to control the rhythm of your breath, as this is not a breathing exercise.
As you breathe in, note that you can feel the airflow as it is going into your nostrils. As you breathe out, note that you can feel the air touching your upper lip as it is moving out. Keep your attention focused on this physical space where these sensations occur. As you breathe in and out, keep your attention in that area. Note that you should try to keep your full attention there, just as you did when you first examined the sensations of breath when you just started.
As time goes by, thoughts will come up in your mind and take your attention away. This is perfectly fine and normal. The purpose of this meditation is to note when your attention has slipped away to something other than that area or sensation of breath, and when you note that, bring your full attention back to that physical space.
Continue this exercise for any length of time you want (1, 5 , 10 or more minutes. Choose a length of time that is slightly challenging but not so much that you dread sitting). Note that this meditation doesn't work as a singular event. Just like lifting weights, it requires regular practice to see any kind of measurable result, so choose a length of time that you can commit to on a daily or weekly basis.
Why does this work?
With this meditation you are basically exercising a separation between your self-agency and your thoughts. When you try to focus, you see that the thoughts come up on their own without any conscious effort. So in a way these thoughts are something that "happens" to you (the conscious you), rather than something that you consciously do. When you practice the exercise of noticing that you are caught in a thought and then letting go of it you develop the skill of detaching from thoughts at will, a skill you'll carry into your daily life. You'll soon see that the faster you detach from a thought the less you identify with it and the less influence it has on you.
What do you get out of it?
This develops several very interesting abilities:
1) You become less vulnerable to being "caught up" in something you don't necessarily want to be caught up in. A big challenge in maintaining focus, motivation and commitment is finding yourself giving in to temptation or distraction. The sooner you catch the tempting or distracting thought trying to take you away, the more easy it is to resist that temptation, or at least drop it early on rather than getting carried off. It's similar to the experience of reading a book, only to discover a few pages in that you've been scanning the lines but not actually paying attention to what you're reading. Instead of noticing a few pages later, you'll be able to notice a few words later.
2) It increases your ability for honest, objective insight into your thoughts. When you detach your attention from a thought, you can use your attention to observe the thought from a different perspective. Questions like "why am I thinking this, where is this coming from?" or "is this line of thought making me happier or more miserable? Is it in line with who I am, or who I want to be?" suddenly become possible, and eventually habitual to ask.
3) You increase your ability to shape the kind of thoughts you have. For example, the mind of a person with low self esteem tends to bubble up self defeating or self deprecating thoughts more often than of people who don't suffer from self esteem issues. As you practice this skill, you will be able to identify such thoughts as they come up and detach from them. The more you do this, the more you train your mind to not generate them in the first place.