If you are passionate about something or a subject if you have the right expertise and you want to share it with people why not share it with audio. A podcast is audio on demand so people can listen to you to what you have to say anytime during the day. They can be running, driving, stuck in traffic or doing exercises.
If you want to build your own authority and credibility you can create your own podcast in a simple niche a focused niche and niche down so you can target a very narrow people of your target audience.
You can build a mass community following you; following what you have to say. You can talk about any field you want. In iTunes, we have 16 categories and hundreds of subcategories, in any field you want to talk about in business, medical, in business let’s say you have careers you have many other subcategories even you can talk about art, music, and others. Only in iTunes we have 525 million subscribers so imagine the community and how you can leverage it.
Why do you need to podcast? One because you are passionate about something and you want to share with people. Two because you have and you want to create your authority and create credibility and more credibility for yourself and three because the audience is there and is waiting for your expertise.