There are many different kinds of use's for a rain barrel weather it be for residential or commercial use.
Most people will use a rainbarrel or a water butt in the UK to collect water from their roof tops via their rain gutters and use this water for their plants, grass, wash their cars, tools or to top off their pools.
There is no rule of thumb as to the Types of Water Barrel you decide to choose.
Please remember that what is clean for plants, is not clean for humans. Use collected rainwater for anything else around your house, except drinking water or edible plants.
So why would you spend time collecting rainwater if you can just turn on water from the tap? In certain areas of the world, its just a matter of survival and the only source that is potable.
Places like India for example,more precisely New Delhi where there's a huge water problem because the water company not having enough money to supply water to the poorest areas,those citizens are left to buy their water from over priced private merchants.
For others its a simple matter of being conscious of our surrounding environment and reducing your monthly water consumption. Why throw your money out the window when you can get rain water for free?
Water is a limited source that we must use with care. Only 1% of the world's water reserve is potable, so the rest of the 97% is composed of the ocean and the last 2% is the Ice at both poles.
Here's a world map showing you the shortage of water around the world, but not because we have plenty of water that we have to waste it.
Rainwater cisterns can hold large amounts of water and are completely sealed from debris and contaminants. Usually cisterns are put underground compared to more simple residential rain barrels that would go under your downspout.
Other types can be plastic tanks that you may have underground (anywhere from 25 to 10,000 Gal) or above ground(325 to 2,500 Gal).
If you have the space for example a farm, or acres of land, why not. It all depends on your needs, your environment, where you live and also your city or town laws, as believe it not some cities may not allow you to install a water barrel. Always verify with your local municipality to make sure you can install a water barrel.