I look at it this way. I could buy a can of Campbell’s Tomato soup and take it home, place it on my stovetop and cook it in the can. Why would I need a pot? Well the answer is "no" you do not. But the can the soup is packaged and transported in is not engineered or designed for cooking the soup, it is designed for packaging and transport. The pot is engineered for cooking, and as such, does a better job.
Audio streamers are designed for transporting audio. Your computer is designed for many things, multi purpose. But it was not designed for streaming audio. Audio streamers do a better job because that is what they were designed to do. It’s simple really....
Do you need a streamer? In the strictest sense.. NO. None of us really needs audio gear. Do you want a streamer for better sound? Only you can answer that question.