Generators are used for many different reasons.
In The Home:
Generators are used for backup when power is lost.
Depending on the size of the generator, you can run refrigerators, washing machines, small appliances and lights to your home. The size of the generator will determine the wattage output.
The more wattage of the generator, the more power you will have to power your home. When the power goes off, a generator will kick in to accommodate your electrical needs.
Homes that have individuals with medical needs that require electricity will want a generator to have power in the case of a power outage.
In a Business Environment:
Generators installed in buildings have an automatic turn on when it senses that the electrical power has shut down.
There are portable generators for short-term power outages. Both types are needed there is a power outage that could last longer than one day. Businesses that rely on power to operate install generators so that they can stay operational during power outages regardless of the duration.
Installing a generator is a project that only a professional, licensed, insured electrician should undertake.