What Happens If You Don't Blip the Throttle?

The throttle blip is used to smooth the transition into the lower gear. Why? If you just depress the clutch pedal, drop a gear and release the pedal, the car is going to buck or jerk because the rotational speed of the engine isn't synchronized to the rotational speed of the wheels when the clutch reengages.

Is blipping the throttle necessary?

Is Blipping Necessary? Some motorcycles benefit from throttle blipping more than others. A big V-twin or single cylinder engine with a lot of engine braking can more easily lock the rear tire if the clutch isn't released carefully, so blipping makes sense.

Do you have to blip the throttle when upshifting?

Unless you are a really slow shifter, you shouldn't have to blip on an upshift. Since with the higher gear your engine speed will actually be lower at the same speed, you need less throttle. It doesn't really matter though.