An uninterruptible power supply is like a generator in a way, but it's definitely not the same. The power supply detects changes in the power it's either receiving or has passed through it (different models use electrical power differently) and automatically switches into a provider mode, with a break of maybe milliseconds in some cases. Some power supplies are on all the time and take over seamlessly, with no break in power. These supplies are often associated with hospitals and other organizations that rely on power to keep people alive, but you can get them for your home as well if you don't want to mess with a generator and have things in your home that cannot go through a power outage.
Medical Equipment at Home
If you've got medical equipment at home that relies on constant power or that needs to be recharged frequently, you can't risk the power going out. A power supply that starts up immediately upon detecting a cut in city-provided power is essential. Generators are nice, but you have to get them and start them manually; if you've got medical equipment to deal with, you want something that starts without your intervention.
Your Home Office or Business Setup
If you do any sort of work from home, you need power. You can't have the power going off and making it difficult for you to continue working. Yes, you can get external batteries for your smartphone and laptop, but if you're going to do that, you may as well have power for the entire home. This lets you continue holding that videoconferencing meeting without missing a beat to wonder why the power went out; you won't really know that the power's gone out, to begin with. If you're designing a graphic on a desktop computer, you can continue doing so and meet your deadline without worry.
If Nothing Else, Your Refrigerator, Freezer, and Temperature Control System
You really don't need anything fancy to justify using an uninterruptible power supply at home. The ability to keep your refrigerator, freezer, and heater or air conditioning running in the event of a power outage is a relief. You won't end up losing food, and if there's a heatwave or cold snap, your home will remain comfortable.
Whether you get a double conversion, line-interactive, or offline uninterruptible power, you can keep your home running as you usually would no matter what happened to your power supply from the city electrical grid. It's worth it to have this backup for your home to preserve your food, work, and comfort.
For more information about UPS systems, contact a local electrician.