If your lights dim fairly often, you should definitely consider one. If you also need protection from power outages, you might consider an on-line UPS instead. Less expensive models will keep the power on during an outage long enough to save your work and properly shut down the machine. Servers should almost always be on an uninterruptible power supply. Networks with file-servers present a case where the higher cost of an uninterruptible power supply is justified by the number of machines which rely on the server for critical information.
Printers draw large amounts of power when first starting up, then go into an idle mode.
This constant shift in power usage can cause damage to a UPS system and limit its lifespan. Phone Ultrafax CCS recommends getting at least a 6-Outlet surge protector. If you wish to have phone protection, the Ultrafax 2-Outlet model is adequate for small systems. A voltage regulator must be matched to your power needs. Most equipment has a sticker near the power plug which tells you how many amps or watts are required.