Without the `mediaproxy` function, Akkoma doesn't store any remote content like pictures, video etc. locally. So every time you open Akkoma, the content is loaded from the source server, from where the post is coming. This can result in slowly loading content or/and increased bandwidth usage on the source server.
If you came here from one of the installation guides, take a look at the example configuration `/installation/akkoma.nginx`, where this part is already included.