A salesman will conjure up all sorts of reasons why not only do you need one, but how spending lots of extra money buys you amazing improvements in audio, video, and your sex life. If I could guarantee the last I could retire. Let's look at them.
Perhaps one of the most useful aspect of a power center, those that sit on a rack, is the feature set you get that some find very useful. Among these conveniences are...
switched/unswitched outlets sequenced turn on and turn off one touch operation for your entire system a fair amount of outlets so you can plug all your equipment into it as well as your cable feeds
Maybe I missed a couple. Virtually all of these units offer some degree of surge suppression and EMI/RFI filtration and they play around a bit with how this is implemented. Because there is no standardization regarding EMI/RFI filtration specs, its very difficult to make comparisons between brands but even 40dB reduction is a 99% reduction in noise and that's fairly substantial.
If you don't need those conveniences, then maybe your needs are more cost effectively served by a plug in surge protection device like various Belkins, TrippLites, Panamax, Stratitecetc. which you can get for well under $100.