WiFi is an essential component in any tablet today. Using it, the internet can be accessed, and the connection needs to be wireless. With wireless WiFi, the internet can be used anywhere there is a suitable wireless internet connection available, not just at home. Bluetooth is a secondary and less important way of communicating.
The Sprout Channel Cubby does come with WiFi as standard. This is needed for some things, including setting the tablet up, but not for everything. Any content that is downloaded onto the tablet, and that does not require an internet connection to work, will continue to work even without one.
Some content (such as online gaming), and surfing the internet, does require a WiFi connection to function, and will not work without one.