Yoga is useful in daily life. We eat food many times a day and do work during a significant part of the day (and night). Then we sleep. This cycle continues. If every one does sufficient exercise every day, then perhaps there is no need for yoga. All people do not exercise their body uniformly. Some persons have some physical disorders and have health problems. Some housewives or fat persons are probably not able to do exercise their body. So there is a danger of obesity.
For such persons, yoga prescribes many asanas (postures). Breathing (pranayama) is also important in yoga. It is usually practiced with very little or no food in the stomach.
Yoga helps good regulation of blood flow in all parts of our body. Yoga helps oxygen flow in all parts of the body. Yoga helps in meditation and concentration. When proper diet is followed along with yoga, it will do good. It is not costly. One could go to free classes in the morning or evening. Or, one could buy a book and practice them carefully.