The benefits of buying your own modem clearly outweigh the charges and challenges of renting a modem from Comcast. When you rent a gateway (modem and router in one unit), Comcast uses your home as a WiFi hotspot. That means others in your direct area (neighbors and people parking near your home) can connect to this network. While this may be secure most of the time, this method Comcast uses will slow down your own home network. There is a way you can change this setting by calling Comcast though.