Suddenly the electricity cuts off, an Uninterruptable Power Supply (UPS) may be the difference between you still working, or you are having everyone just sitting around till the power comes back on. I also do believe that the performance and longevity of your Point of Sale equipment will increase if you use them.
Here are some tips if you are interested in such technology.
1) You need to decide how long you need the UPS to function, in the city often the power goes down for a few minutes, but in the country, it can be an hour. Generally, it is best to spend a little more and get something that lasts a bit longer. No one is going to complain if it is slightly too loud.
2) They need testing. I have seen the battery inside fail with no warning. They are easy to test; just switch the power off. One problem with UPS, far too often they fail straight out of the box, so they need testing.
3) Check for noise, some of them are very nosy in operation