You can plug your amp head in to it, your cell phone charger, a desk lamp, a portable fan, strobe lights, etc. its just a power outlet.
Now that said, some have lights which are very handy, and others have a display that reads the voltage you are getting from the wall. Mine has plugs for digital components - no idea if these do anythung different than the regular plugs.
I bought mine for $160 before researching. Its pretty heavy too. There's definitely more stuff inside it than a power strip pictured above, but general consensus is the rack mounted ones do the same function but for 10-15x the cost.
I still like mine for the lights, the 8 (I think?) outlets in back, 1 outlet in front, and very long cable to reach the wall.