I have used an APC UPS for many years. Protection during a power outage is actually my
minor reason for owning it; we don’t have blackouts often.
The major reason is for stable, clean power for all of the electronics.
Although drives can be corrupted by a power outage, other devices including computer power supplies are also vulnerable to damage from
unstable power (link is a PDF file). Significant over- or under-voltages can degrade circuitry and shorten the life of components. Although everybody knows about a UPS keeping power going during a power cut, for me it’s just as important that a UPS feeds electricity to connected devices at a voltage, frequency, etc. that are always consistent, even when mains power is erratic, something we normally don’t notice. Noise filtering can also benefit some devices (“Data corruption is one of the most common results of noise.” — from PDF linked earlier.) I know this is anecdotal, but I like to think that the reason my 2006 Mac Pro still runs perfectly today is that it’s been on a UPS its entire life, isolated from electrical issues and always given stable power.
I do use a laptop most of the time now, so yes, it has a built-in battery backup. But on my desk, the laptop is connected to storage and backup drives, a film scanner, displays, the hub that connects then all to the laptop, and many other devices I would like to keep going for as many years as possible. I don’t want those electronics continually exposed to potentially damaging power fluctuations, so anything I want protected is on the UPS. The cheaper/more easily replaceable devices are on ordinary surge protectors.
In the living room, I used to have a problem where if the refrigerator motor came on, the TV would slightly glitch and audio cut out for a very brief moment. Going by what I had seen in the studio, I finally put the living room gear on a Tripp Lite UPS. It isolates all devices on it and regulates the power enough that the TV is now stable, no more problems. I also have an old Mac mini as an HTPC/server in the living room media cabinet; another consequence of the UPS is that Mac has been spectacularly stable, now approaching 140 days continuous uptime, just sleeping when not in use.