In the first part of his article on leveling in MMO's, game journalist Petter Mårtensson points out the relation between level caps and dominant business models in MMO's as they contribute to lengthen gameplay artificially.
To lengthen gameplay in an "ordinary" single player game, it can be as easy as copy-pasting corridors, enemies and sometimes even puzzles. But those games have a limited length of gameplay more or less built in, sooner or later they will run out of story or playable levels. The player will be done, the game will be ejected from the disc drive of whatever machine has been used and put back into the bookshelf. Game over, everyone is hopefully happy and satisfied.
Not so much for the MMO-player, or the MMO-developer. After all, a MMO is supposed to be played for a long, long time. Hopefully for many years, offering the player a world to move into. A MMO needs to be designed to be addictive, and even though the ethics of this design have been debated back and forth for a long time, it's a fact of life that every developer that wants to get in on the genre needs to take into consideration. It also means that gameplay must not only be stretched for a couple of hours, it needs to be stretched indefinitely.
But we already know this, if you've ever been in contact with an MMO (and seriously, I know that you have a World of Warcraft account, active or inactive, confess!) and thought about its design, you've considered it. If you've ever visited an official MMO forum, those cesspools of flames and trolls, you've seen fans bicker about running out of new things to do, new dungeons to conquer or content to tear through. It's all about lengthening gameplay, to keep people interested enough to keep the money flowing out of their pockets for the same game for months on end.
Let's say you're developing a MMO (everyone seems to be, these days). You have all kinds of great ideas, fascinating new mechanics and ways to revolutionize the genre. The only problem is that you know that if you let the players run rampant on your game, there's always the chance that they will play through it like a single player game. No matter how many quests, dungeons, raids, Player versus Player scenarios or deep economic systems you put in place, there just won't be enough to keep people occupied long enough for you to develop more of it. In short, you need to lengthen gameplay artificially, not by actual gameplay elements, but by gating the content you have. Keep those pesky gamers occupied elsewhere, buying you and your team time.
Luckily for you, there's already a tried and tested system that no one will even react if you use. Leveling. It's an awesome system, it's been around for decades in both computer and pen-and-paper RPGs, and almost every MMO ever released (with a few notable exceptions, of course) use it in one way or another. So put that in there, let the player start out at Level 1 and then have him/her quest or grind for experience points until he/she reaches your defined "level cap". Let the player feel like he/she is "growing in power", in order to get ready for the stuff waiting at the top - the mythical Holy Grail known as "end-game."
Petter Mårtensson is a games journalist from Sweden, specializing in (or obsessing over, depending on who you ask) massively multiplayer online games. Most of his journalistic work is published in Swedish, but his personal blog - Don't Fear the Mutant - is written in English.