Some people might have observed that when in cars, after changing engine oil and filter, when it is started, the red oil pressure light remains on for just couple of seconds. This is due to the delay in oil pressure restoring due to empty filter and probably empty oil lines. So in cars it is generally not recommended to rev the engine when starting. But that is just for few seconds. In motorcycles case, you normally don't replace the oil filter with every oil change, so it may not be required at all for motorcycle engines. But it is generally a good practice whenever you start the motorcycle or car to give few seconds idling or low rpm running just to enable oil pressure to build up and let it circulate through the engine before flooring the accelerator.
