What is the purpose of whipping a bike?
Spinning wheels have gyroscopic effects. Whipping the bike can be a way to reposition the bike so that when it comes out of the whip, it is in an orientation that wouldn't be possible going over the jump dead-straight. This effect is large in the case of motocross.
From a BMX perspective, it is very important to land on the backside of the landing ramp with the proper bend in your legs so that you can get the maximum &quot;pump&quot; off the landing. In some cases, especially in the case of a short landing ramp, it can be advantageous to do a slight whip and therefore land with the bike at an angle. This can get you more pump than landing perfectly straight. If you watch people negotiate a street spine, for example, you will see that it's downright awkward to go straight over without doing a whip.
Also, there's often a corner and a berm shortly after a jump, so a slight whip can set you up for what comes next, vs. landing perfectly straight then having to muscle the upcoming corner.