This would just affect the performance of the network, in other words: your internet connection.
Connecting directly to your modem or router via a hardwired connection (physical network cable) would eliminate any connection drops associated with wireless traffic. Wireless connectivity issues can occur for a number of reasons, including if you are too far from the router, dead spots in the home, or radio interference.
Yes, for example if you have a microwave between your cell phone and your access point, your connection will suffer until the microwave turns off. Wireless interference / fits and starts / connection drops are all influenced by variables such as other wireless devices, thickness of walls and distance from your access point. A hardwired connection is not susceptible to any of these variables.