No it is not absolutely necessary

By just using oil and cooking with it, you will over time "Season" the pan. It's just not a great way of doing it

You will get better results following the basic steps documented on SA or elsewhere e.g. http://cooking.stackexchange.com/questions/641/whats-the-best-way-to-season-a-cast-iron-skillet

Basically all you need to do is; clean the pan, oil it, heat it to a high heat. That's not too tricky, is it?