As the name implies, an off-gird location is completely disconnected from the utility company. The reasons for going off-grid are many. Many of the most dedicated off-grid patrons are those that have committed to lessening their impact on the environment by totally committing to clean, renewable energy sources. In certain parts of the county, there are large communities of independent souls who have chosen to live disconnected from the grid and do so effectively by limiting their power consumption and using renewable energy sources such as wind and solar power.
In other situations, such as remote cabins or vacation properties, there is no chance of ever connecting to a commercial grid and the only alternative is renewable energy or generators. Even if you rely primarily on solar power at your vacation cabin, you will probably need to add a generator for periods of very high usage, and during periods of cloudy weather.
An off-grid system is more complex than on-grid, and considerably more expensive. An off-grid system will require additional components like batteries, charge controllers, and perhaps a generator. This also adds to the maintenance issues that the owner will be required to take care.
All that said, off-grid technology definitely does work, and in certain situations may be the only available option.
