There are certainly uses for Wi-fi.
Stuff like Quake, Quake 2 and ZDoom can now be played online.
The lack of Wifi meant that i could not really post my Rule34 image downloader OPK because telling people to get an USB C dongle is not worth it.
As iball mentionned, it could also be used to transfer files to the console itself.
Emulators could in theory be updated for local or online play. However, this requires having experience with networking, and i'm certainly not knowledgeable when it comes to that stuff... (aside from libcurl i guess but that's not really deep networking stuff)
Yeah for the most part, it was seldom used on the GCW0. (although this was mostly because most of the GCW0s out there died or had hardware issues so it wasn't worth using it)