So you think you might want to play a mage. But why? Why would anyone play a mage, when you could play a vampire or a shape-changing breed? After all, there are dozens, if not hundreds, of channels with a vampire theme; the vampires secretly run the whole world of darkness... they believe. There are almost as many changing breed themed channels; the shifters may not run the world, and may be hard-pressed to keep it from being spoiled, but corruption hasn't completely consumed the world of Darkness and the fight for Gaia has not been lost so long as even one of them still draws breath. So, in a world where it seems that everyone else can flex their supernatural muscle with little thought of repercussion, why play a being who risks having Reality itself kick him or her in the teeth whenever he or she attempts to change things to more suit his or her preference?
Perhaps the allure of magic has something to do with it. Some say that mages use magic. Other claim that mages are magic, or the embodiment of magic: unknowable, unpredictable, by very definition a wild-card in the world around them. Mages champion a sense of wonder in an increasingly jaded world, or they silently tend to the hidden underpinnings that keeps the Real in Reality more or less consistent. And they do so in ways that can be so subtle as to elude notice, or teeter on the uttermost edge of incredulity and wonder, transforming the impossible to miraculous, the miraculous to tentatively plausible and merely difficult, and the merely difficult into the commonplace by degrees of acceptance.
And that's the sort of philosophy you might expect to hear in a fantasy world, as spoken by one of the characters in that world, but we're not those characters. When you consider the real-life motives of the real-life person sitting at the keyboard, I'd imagine the bottom line is that a person would play a mage for pretty much the same reason that a person would play anything else: to have fun with old and new friends. Games and gaming are supposed to be fun, after all.
Repeat after me: first and foremost, the game should be fun for all. Maintaining game balance and playability helps ensure everyone has fun. I feel pretty safe in saying that acting in a manner that breaks the game or monopolizes game-play probably won't be appreciated by other players or gaming staff. Playing in a manner that trivializes other players wins hostages, or maybe hirelings, not friends or companions. Play gently, play cooperatively, and everyone has fun.
In a perfect world, I imagine that we play in the channel because we enjoy gaming together and we live far enough apart that getting together for a weekly table-top gaming session isn't practical. In a perfect world, I'd suppose that our personal goals and character goals are compatible enough that we can all have fun while exploring and pursuing and cooperating to reach as many of those goals as possible. In the channel, as in this thing we call real life, I believe that the greatest potential for fun can be realized when we cooperate and work together. While we might do our best in and out of character to make the game world around us a reflection of that perfect World of Darkness, the truth of the matter is that the game and the game world is a work in progress. Chances are good that we'll accidentally tread on toes (sorry!), and occasionally working together might involve setting aside or postponing individual and mutually exclusive goals. And... in the game, as in life itself, cooperation and balance are more easily said than done.
Why do I repeatedly mention cooperation? Because with their ability to dynamically redefine the Reality of the game world around them, few character types can match mages for sheer potential to overpower and unbalance a World of Darkness game, to abruptly squash a story-line in the very formative stages, and to pretty much guarantee nobody else has much fun. I've heard that so-called "power-gamers" prefer to play mages for this very reason. If that nasty rumor has more than a grain of truth behind it, that could well explain why there aren't a lot of exclusively mage channels, and why many World of Darkness channels don't allow mages, period. And that would be a place we don’t want to go.
The other theme I hear often is that Mage gets complicated and confusing. Unlike books for other classes which have their specific rituals and effects spelled out, the Mage book marks the starting point of an infinitely complex open ended system. The limits tend to be the imagination and audacity of the players, and those limits are tempered only by consideration for other players and whatever checks and balances an ST chooses to employ. Can a clever player come up with something completely unexpected, staying within the guidelines provided? Absolutely! Should said player be allowed to derail a storyline and end game-play for all? Absolutely not!!
Neither the gaming staff nor all the players are familiar with every book or rule ever published by White Wolf. There's a whole lot of grey territory. If an issue or question comes up, cooperate with the gaming staff to resolve things quickly and in a friendly manner. Keep in mind that while you attempt to make your point or explain what you've done, role-play comes to a complete standstill for everyone else involved, and waiting for an hour while two people argue about some unexpected result isn't much fun.... If requested, a quick canned explanation or description goes a long way towards keeping things interesting for all.
If your idea of the ultimate fun gaming experience is to find any excuse to soundly thrash senseless every being you encounter in the gaming universe, to subjugate everyone and everything your character encounters, to kick butt and take names, then I'd invite you to reconsider playing a Mage; that gaming style is more suited to playing a stereotype Garou shock-troop warrior, an avenging Hunter, or an NPC. If that's you're preferred game style, expect life to be short, and life insurance for your character to be generally unavailable... though a bookie might be willing to give you odds on surviving for a year or more in game-time. (Expect it to be a long shot.)
In a nutshell, playing a mage in any channel can be summed up thusly: play nicely, or get kicked out of the sandbox!