Known by many names, I personally have known and spoken of it as "power-leveling". Greedy Goblin calls it "boosting", and he doesn't like it one bit. Call it tough-love, but according to Greedy Goblin, you should never help a friend or family member level because they apparently won't grow up to be big and strong if you do.
I have agreed with many of Greedy's posts in the past, but on this one I just don't see eye to eye with him. His stark, take it or leave it, logic simply doesn't add up in most respects. Take for instance a guild who asks someone to re-roll and play another class that is needed in the raid. Ignoring completely the question on whether the guild owes said person support in that leveling process, isn't it in the guilds best interest to give it in order to get make that class available at the earliest opportunity? Asking someone to re-roll is most likely a last resort, taken only after they had been unable to find a qualified player of that class previously. And sometimes the "bring the player, not the class" just doesn't work out as intended.
How about a situation where a group of friends convince another friend to transfer servers in order to play together. Perhaps that individual could transfer a fully leveled character, but what if they want to play a different class or can't transfer the character for whatever reason? I suspect the friends would probably not completely power level the other player, but would one really expect to transfer to a new server at the coaxing of friends and then be left totally to their own devices for a few weeks while they level to 80? Would the friends not want their friend to get to 8o as quick as possible so they can play together?
Does 1-79 matter that much that helping someone destroys the game? Greedy certainly alludes to that, but I think it's clear that isn't the case. WoW really begins at end-game. The path from 1 to endgame is just an obstacle that must be overcome as quickly as possible in order to experience it. Any argument that someone power leveled won't have learned their class adequately are completely without merit. Someone can be just as much a noob at 80, having taken the time to level on their own as someone who was power leveled the entire way. What matters is the person behind the keyboard. If they are in any way competent and have an ability to read and comprehend then they will shed the noobness regardless of how they get to endgame.