OK, guys -- please forgive me, because I haven't owned a bike with a chain for a very long time -- probably in the 80s. Why do I need to replace a chain and/or sprockets? What would happen if I didn't?
You would only have to change them when they are worn past their service limits. Please see the manual for the procedure for checking wear.
If you continued to ride with overly worn chain and sprockets, you would eventually loose the ability to transfer power from your engine to the rear wheel (best case), and you would stop forward motion due to the sprocket teeth being worn down to the nubs.
The worst case - the chain snaps and breaks while you are traveling at 70 mph, and it either gets tangled in the rear wheel, locks it, and spits you off the bike onto the concrete at a high rate of speed - Or the chain breaks and it whips onto your crankcase and knock a hole in it, causing loss of engine lubrication, oil spillage, etc. and loss of forward motion, need for crankcase repair or replacement.
Or the chain could break and just fall off the bike, causing you to gently coast to a stop.