Yes. It was my understanding too. I began running a skimmer on that tank from the get go. The skimmer ran for 1 year. Problem was, it was filtering too much nutrients. I couldn't get my po4 or no3 up. Skimmers are also great for adding O2 to the tank.
Originally i was going to tear down my old 20 and get my new 30g going. Not everything went as planned. But, i did remove the skimmer and noticed the 20 gallon began to thrive again. I realized then that my bioload in the 20g was never a problem. Most likely wasnt necessary to have a skimmer, yet.
I think we recommend skimmers for newbies because well, I've noticed, they go a little overboard with fish population. Often times getting fish rated for 75 gallons plus. Those types of fish produce large amounts of waste. I think skimmers are a must, however i think they are as much a necessity as dosing. Meaning, you may not need off the bat, but later on for sure.
My new 30g tank is 100% dry rock cycled without all the micro fauna like live rock. The biology in this tank doesn't oxygenate properly and therefore my skimmer helps oxygenate the water to keep the fish from stressing.
Hope this helps.