Do UPS increase the performance or life expectancy of the hardware connected to it? What if the UPS has a built in line conditioner?
This is not necessarily true: "a UPS is simply a giant battery with a plug-in and plug-out that provides the same voltage and current as the mains otherwise would under normal circumstances." Many UPS models regulate voltage. You'll typically see these referred to as line-interactive and online UPS. An online UPS completely regenerates incoming voltage and so that the UPS output is plus or minus 3% of the nominal voltage. The most basic home UPS models are standby UPSs that don't do much or any voltage regulation. If you install a UPS that regulates voltage, then your equipment will get a steady diet of quality power instead of a poor diet that will impact equipment over time. Therefore, a good UPS is a great investment when it comes to extending hardware life.
This might be a helpful resource, the Eaton UPS and Power Management Fundamentals Hanndbook. http://viewer.zmags.com/publication/cd2a856b#/cd2a856b/1
Not directly no; a UPS is simply a giant battery with a plug-in and plug-out that provides the same voltage and current as the mains otherwise would under normal circumstances. It certainly won't increase the performance of any of the hardware, but it may have a slight positive effect on life span if you have a low quality power supply as it should provide some amount of mains filtering that will leads to a smoother current. However this is something most decent power supplies do themselves.
It might however save your hardware from damage in a non-normal environment, for example most UPS's are surge protectors by their nature (or contain surge protection hardware) and as such the UPS will eat a surge opposed to your PC/Server/TV/whatever. Additionally when a UPS is performing its designed roll (providing power during a black/brown-out) then it allows hardware to be shut-down correctly, as certain items are particularly at risk during a sudden power loss (Hard drive for example).
In short, Performance No, Life expectancy Maybe