There are a number of reasons you may want to invest in a UPS system but generally it is to protect your critical systems from the effects of power failures, voltage dips and power anomalies.
During a power failure your IT systems, process control and telephone systems would not operate, leading to missed calls/sales/transactions, loss of product/data or loss of staff productivity.
During power anomalies all circuits may be affected requiring systems to be re-booted, cleaned and data re-entered. The time and inconvenience caused can be a nightmare for any business.