Running a protein skimmer on a small tank is optional, as long as stocking is light to moderate and water changes are performed on a good routine. If you're referring to your 75g, a protein skimmer would generally be considered a good piece of equipment to have for that tank size.
Basically, protein skimmers help remove organic waste from the water. While there's so many companies that make skimmers, there's really only a few different designs, and each has its own pros / cons. Nonetheless, despite a looking similar, many cheaper "knock-off" skimmers tend to not operate as efficiently as some of their pricier counterparts.
If you have a sump for your tank, there's a seemingly limitless number of in-sump protein skimmers. If you need a hang-on model, the choices are a bit more limited, but there's still some good ones out there.
Skimmers don't require much in terms of set-up... just put it together and plug it in. They all do require some adjustment to get it skimming properly, but most don't require frequent tweaking after initially dialed in.
