Not sure what you mean. Can you be more specific? Fitness isn't the same as exercise. Neither is necessarily the same as healthfulness. What it brings depends on what you're seeking from it.
I'll take a stab at this really general question. I'm not exactly sure what you are looking for but exercise and fitness are an important part of life for people that are medically cleared to participate in it. It brings on better health when done correctly such as cardiovascular health. It brings us a better frame of mind following exercise as it is known to be calming. It can be social if you work out in a group which enhances one's life. It helps you maintain a proper body weight which helps not only to maintain your overall health but to keep diseases such as diabetes and others at bay. Exercise can raise your HDL cholesterol which in turn helps control your total cholesterol numbers stay within the goals set by doctors.
For most, it makes us feel better. So, it's a good thing to do.
Exercise delivers oxygen and nutrients to your tissues and helps your cardiovascular system work more efficiently. And when your heart and lung health improve, you have more energy to tackle daily chores.