There are many benefits from being fit. 

Being fit has many short-term benefits, such as an improved sense of well-being, and long-term benefits, such as reducing the risk of suffering many debilitating diseases.

Short-term benefits of fitness include:-

A healthier heart;

Healthy muscles, bones, and joints;

Increased burning of calories;

Better ability to cope with stress;

Improved ability to fall asleep and sleep well;

Helping older adults become stronger and move around more easily;

Reduced feelings of depression and anxiety;

Increased energy;

Increased mental acuity — sharper and faster thinking.

Long-term benefits of fitness include reduced risk of:-

Dying early;

Coronary artery disease;

Dying after a heart attack;

Developing high blood pressure;

Developing type 2 diabetes;

Developing colon and breast cancer;

Becoming obese;

Stroke.

In addition, physical activity plays a role in the positive outcomes of:-

Atherosclerosis;

Asthma;

Chronic obstructive pulmonary disease (COPD);

Type 2 diabetes;

Osteoporosis;

Surgery and injury;

Gallstones;

Low back pain;

HIV and AIDS;

Rheumatoid arthritis;

Multiple sclerosis;

Other benefits of being fit include an inner glow resulting in improved facial appearance and body composition (how much muscle and fat you have), and enhanced social life, and increased stamina.
From the foregoing, it is apparent how vital it is to engage in some regular fitness program to help provide a resistance against these illnesses.

If, however, you have conditions that may make physical activity risky for you, such as coronary artery disease, high blood pressure, heart valve disease, or diabetes, talk to a health professional before starting a fitness plan. It is likely that he or she will still recommend some kind of physical activity program, but your plan may need to be matched to your specific needs, and you may need to be more watchful for signs of illness or injury