This. If you're not using a steel ever than you're missing out. They maintain the edge so you can go longer between sharpenings - when my boning knife starts to get dull while butchering a few swipes on the steel gets it cutting nice again. They don't replace proper sharpening when the time comes, but they will extend the period you can go between sharpenings.
If you're trying to SHARPEN a dull knife with a steel you're doing it wrong...
Yes, technically "sharpen" was the wrong word to use in regards to "sharpening steels". I never use them, never will. I prefer to strop my knives every so often depending on the hardness/edge retention of that particular steel and rarely have to take them to a diamond or other type of stone. A few seconds on the strop and they are hair popping sharp again.