Wi-Fi is very helpfull for the wii because, You can benefit from Buying able to use the shop channel and purchase virtual console games, The virtual console will be a very helpfull feature as from their you can sometimes get a new channel for the wii, also, many of the channels use wi fi such as the everybody votes channel, news, weather forecast, internet, mii channel.
Also, the wi-fi is there so you can get wii system updates/firm ware updates.
These firmware updates basically add new things to shop channel (such as new channels ready for purchase), firmware updates also update your wii with certain bits of software helping your wii, improve its performance or stop bug's or modders getting into the sytem.
Coming soon is online games which will use the wi fi feature to play other wii owners online through wi fi.
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