This is a fairly indispensable accessory for oiling the carbon steel and cast iron frying pans and skillets. In my particular case I use it with YAMADA carbon steel skillet as a time-saving accessory when re-oiling the skillet prior to storage.
Since all carbon steel and cast iron cookware will rust unless properly maintained, it means that after each use you must wash it thoroughly as soon as possible and then re-heat the skillet and apply some cooking on the entire surface before putting it away. This basting mop makes it easy and fairly economical, since you only apply a thin layer and very little oil is wasted. Note that you MUST wash the mop prior to the very first use. Dry it thoroughly afterwards and you're ready to use it.
I don't use mine for cooking purposes, since I tend to be fairly liberal at using olive oil while cooking :)