Bikes don’t like dirty roads. All those moving parts suffer from being exposed to salty, wet roads. If left to its own devices, salt will begin to corrode and rust your shiny steed. It’s amazing how quickly a chain can turn a nice shade of orange after a winter ride.
It’s a good idea to get into the habit of giving your bike a wash down and dry, there are lots of specialist bike cleaning fluids on the market but a bucket of warm soapy water and a sponge and soft brush is better than nothing. A clean rag will be fine to dry off.