When you are blogging, you absolutely need free images – that you can use legally. When you are podcasting, you need a soundeffect or a piece of music once in a while. And even when you are creating videos, you might from time to time need a snippet of video that you can’t shoot yourself.
In short, when you are creating anything for the online world, you absolutely need third-party content to make your own content awesome.
If you don’t know what you are doing, you are entering a legal minefield. And if you aren’t careful, you may receive a friendly letter from a lawyer with a DMCA takedown notice. Or worse.