There are times when the hard drive can become corrupted if the power was to drop. Its not something that happens most of the time, but it does happen.
Keeping full system backups is often a better solution than a UPS. In my case, I bought a HGST 2TB hard drive for $70, and a good backup program for another $30, and I have set it up to make a full system backup to the 2TB hard drive three times a week. So if my 1TB SSD dies or becomes corrupted, I can get back to where I was no more than 48 or 72 hours ago, and I also have 2 other backups from the same week.