iOS9 has introduced a new feature called "Wi-Fi Assist". This feature is designed to overcome weak Wi-Fi signals and allow your iPhone or iPad to automatically use your devices mobile data instead.
A problem with this is that you may not be aware of this and if you are updating apps or watching videos, you could very quickly chew through your monthly mobile data allowance.
If you have multiple wireless access points with different names around your home, you may not be getting the best Wi-Fi experience that you were expecting by having them
The reason for having multiple wireless access points will usually be to assist in overcoming either of the following:
The problem with most devices however, is that they will most likely store Wi-Fi points in a preference list and will use this instead of connecting to the strongest signal available.
To overcome this issue, it is recommended to use a single name for all wireless access points in your home and use the same password/passphrase. Once this change has been made, your device will connect to the wireless access point delivering the strongest signal.