When Wiimm and me started working on Wiimmfi, this forum was where we exchanged information and documented a bunch about the process of creating Wiimmfi. And as both this forum and the Wiimmfi server is A) running on the same physical machine and B) are both run by Wiimm and me, we've decided to not bother implementing account registration, password resets, account profiles, and so on for Wiimmfi alone and instead made it that you can use your existing account on this forum to log in to the Wiimmfi webpage.

For normal gameplay on Wiimmfi you do not need to have your console linked to an account. But it's helpful for stuff like statistics (for example, if you're logged in on Wiimmfi and go to wiimmfi.de/stats/track/mo you can see all the tracks you've played recently), or for additional features like OPENHOST (managing your friend list / who can enter your friend rooms through the Wiimmfi webpage instead of through the game).

It also allows you to participate in beta tests - sometimes with new features or bugfixes we decide to first roll them out to a small number of testers and then later (when everything's been tested) to everyone, and on the Wiimmfi page you can choose which consoles should get these beta versions.

As for friend code exchange, I believe most of that has now moved to Discord and game-specific Discord channels.