WiFi extenders are incredibly versatile network products. Below are some ways in which they are used:
Range Extender: Extends the range of an existing Wi-Fi network or hotspot
Access Point / Wired Network Converter: Provides wireless network connectivity to wired Ethernet devices
Wireless Bridge: Wirelessly connects 2 or more network segments
Minimize Mobile Broadband Data Consumption: In areas where public Wi-Fi is available (and/or Mobile Broadband is not) simply connect the Range Extender to the Mobile Broadband Router (i.e. Cradlepoint Routers), and switch your internet source from Mobile Broadband to Public Wi-Fi without changing settings on multiple connected laptops, smartphones, etc.