It depends on your definition of sore. If your muscles are telling you not to ride but you ride anyway, your not doing yourself and favors. You can actually make things worse. However, if your a little sore after the previous day of doing a 100 mile ride or something, maybe opt for a recovery ride the next day if you feel like you want to ride. Usually a recovery ride is at a pace you could carry on a conversation. Either way...you do want to budget a day of rest at some point to give your muscles a break. Make sure you are properly warming up and cooling down your muscles and well as ensuring proper strectching. Always remember that recovery is the most important part. If you don't recover properly, your work out is pointless. Recovery= Proper streching/Replacing lost fluids and calories/protien intake.