Seriously, what happened was that a model with flight could "fly high," sacrificing its movement to be placed off the table. In a subsequent turn, a flying high model could charge anything on the table or just be placed wherever you want.
If your opponent had a model flying high, your own flying models could fly high and charge it, fighting a round of close combat off the table, with the combatants not remaining locked in combat. If the flying monster died, any rider would plummet to its death.
Therefore, if you flew high before your opponent did, you would get charged and your mount would have to weather the attacks of both character and monster before having a chance to strike back. This oftentimes resulted in a dead mount and an equally-dead character and as such it was only ever really used against armies that didn't take a flying monster--and every army could.