@tofu UPSs have some glitches, but the benefits of the power conditioning they do (the good ones) outweigh the trouble of the rare glitch. For example, reducing wear and tear on the electronics they power. Also, the performance of some electronics is highly sensitive to the quality of power provided (e.g., no under- or over-voltage conditions). I don’t rely on the UPS for surge protection. For that, I use upstream Tripp-Lite outlets.
@tofu It depends on your local power system. At my house, I see frequent under voltage conditions. Also, some devices are more tolerant than others. You’ll find power conditioning in pretty much all data centers.