In what sense? Your question is kind of vague without a little background.
Allowing guests on your WiFi? - use a Guest WiFi feature on most routers unless your guests need access to stuff on your network. Some routers allow guest WiFi users to access the LAN devices and services, but by default keep them isolated, so you could toggle the isolation setting if someone needs access to file shares, Airplay devices, etc.
Allowing neighbors to use your WiFi instead of getting their own internet service - never.