If you rely on Wi-Fi networks a lot you'll likely add a lot of Wi-Fi networks to your phone over its lifetime. But the more Wi-Fi networks you add, the more effort Android takes to connect to a Wi-Fi network as it goes through the list of added Wi-Fi networks to see if there are any hidden networks to connect to first before presenting you a list of all Wi-Fi network SSIDs being broadcasted. In short, you want to keep you saved Wi-Fi network list short so you save battery life when connecting from network to network. You can normally remove Wi-Fi networks by clicking on Settings/Wi-Fi and pressing and holding onto a Wi-Fi network and click on Forget in the popup. This seems to work for "out-of-range" networks but not secured networks that are in-range of your home. I've assigned our Wi-Fi Analysis Group (WAG) to see if there is a solution for that, but they have so many important things to do, we have no estimated time of when they might figure it out.*
* The WAG director informs me he believes there is no solution because what the phone actually is doing is listing all wi-fi spots in range. And you certainly don't want to exclude secured wi-fi spots because many of them will be ones that will give you the password.
[Note: This applies to Android. Likely, there's a similar iOS way to accomplish the same thing]