One way to denoise an image could be to remove high frequency detail from it

Since adding noise increases high frequency content and results in a larger file size, it seems like it's not really useful. What are some reasons why we would increase noise of an image? Is this related to "sharpening" filter on slide 62?

Adding noise is like adding high freq. energy. But we still can see the edges of the original image(red box). So the idea is, how about we remove the high freq. components. Would we still be able to recognize the original image?