There’s some myths and half-truths about cast iron skillets, but I am certain that seasoning the skillet changes the taste of the food. If done right, it definitely changes taste for the better and makes the cast iron skillet easier to clean.
Image via Wikipedia
The basic premise to seasoning a cast iron skillet is that you’re trying to get oil into the pores of the cast iron. One of cast iron’s properties is that it is a porous metal. This is what allows it to hold an even temperature for so long. Those pores hold heat. To change the level of the heat, it takes time. Minor fluctuations in the heat source will not effect the cooking temperature. Those same pores will hold anything that comes in contact with them. Use soap on it, there’s going to be soap in the pores, so don’t use soap on cast iron! When heated, the pores of cast iron open up. If you put oil and seasoning into the pan while it’s hot, it’s going to hold them in the pores. The right seasoning, like bacon grease, will release a light bacon flavor into the food being cooked
Here’s a video showing one of the many, many ways to season cast iron.