Essentially, a UPS is a big battery pack that can keep things running in the event of a power failure. Think of it like those little USB battery packs you plug your smartphone into, only much, much larger.
It sits between the mains power supply and your electrical equipment, acting as a passthrough while charging itself under normal conditions. If the power goes out, the battery will then use its charge to keep your electricals powered up.
Large companies will use a UPS to keep their essential systems running in the event of a power cut, but much smaller options are available for the home and small office environments. It's something if you've considered at all, you should definitely invest in.
Or rather, it's something you should invest in if you have anything in regular use that isn't portable, such as a laptop or tablet, with their own built-in batteries. It's a waste of money if you only use something like this.
Desktop PC equipment and many other electricals for that matter are sensitive to sudden surges or complete cut outs in power. Once or twice you can get away with, but if losing power is a frequent occurrence then having a UPS in-between will protect your valuable equipment from both. Whether it's frequent power cuts or a toddler who keeps turning off the plug, you'll have piece of mind that when the worst happens you have a backup.
A UPS will give you piece of mind that your expensive equipment is being looked after
What you'll get from a UPS is time to correctly shut down your equipment if you've lost power completely at the mains. The size of the unit you go for and how many devices are connected will ultimately determine how long you have, but you'll have an opportunity at least. This is the main benefit to having a UPS in the home; you can shut everything down correctly and minimize your chances of serious issues. Some will even have special software to shut down devices like NAS drives properly without you having to do a thing.
It all sounds rather expensive, and as such might be something that keeps getting put to the back of your mind. But, as with most technology, there's something for everyone. UPS systems don't have to cost a fortune, with some very affordable options out there.
The bottom line is that we'd certainly recommend a UPS to anyone who has an amount of frequently used, sensitive equipment such as desktop PCs and games consoles. Give yourself the time to make sure they're shut down correctly while protecting them from surges during use. Most UPS units will also come with some kind of insurance from the manufacturer, so that should an issue arise as a result of use, you have that little extra piece of mind.