Bungie Pro is a file storage and sharing solution that is not in any way, shape or form integral to your Halo 3 experience. Simply put, it's the expansion of storage for your files, these could be Films, Clips, Screenshots, Map Variants, Gametypes or some combination including some or all of the aforementioned. The default File Share for players is six files, Bungie Pro expands that file share.
That File Share is stored on Bungie.net in both standard and expanded forms.
Here's an example of a File Share with barely anything in it, mine. Both the standard issue File Share and Bungie Pro both allow players to tell their 360 to download files from Bungie.net.
Many weeks ago, Roger Wolfson, a super genius working on all manners of Database and information tracking for Bungie Studios checked in with a Weekly Update about Bungie Pro. We're revisiting that thorough description below.
"Hey folks, Roger here. The Bungie server-programming team has been
working on some cool new features to integrate with Halo 3, and it’s
time to spill some details (all of which may, of course, change before
launch. Or even after, really; anytime we have a whim to mess with you
guys.) Topic of the day: file sharing. You saw the basics of this
during the public beta: custom game and map variants, screenshots,
saved films and film clips can all be uploaded to your personal (but
public) file share on our servers. The current plan is that everyone
with a copy of Halo 3 and an Xbox Live Gold account gets 6 slots where
you can place up to 25MB of these files to share with the world. Saved
films take up the most space, and 25MB should be enough to hold several
longish 16-player games. We don't think the average user will be
hurting for space.
"But wait!" you exclaim, "I'm not a merely *average* user! I plan to
win every motion picture award there is with my exquisitely
choreographed, epic-length saved films!" And *that* is where Bungie Pro
comes in. "Bungie Pro?" you ask, an eyebrow raised. "I'm listening."
While we can't give huge amounts of free storage to every one of our
users, (note that unlike webmail sites, Bungie.net remains ad-free,)
we're happy to accommodate power users with a premium storage option
that we've dubbed Bungie Pro. Inside your file share, you'll find a
button that will lead to an Xbox Live Marketplace panel, offering you a
one-year "subscription" to Bungie Pro for a planned 750 Points. Buy
this, and for the following year, your file share will balloon to 24
slots and 250MB. At the end of the year, you'll be asked to either
re-subscribe, or else bring your share back under the default limit
before you can upload new content. (750 Points comes to about 78 cents
per month, by the way.)
"But wait!" a much smaller set of people calls out. "Why pick 24 /
250MB?" That's really a design decision - we figure that users of the
file share don't want to have to page through endless lists of other
people's files to see if there's anything good. Keeping it limited will
make content authors do their part to keep their shares clean of the
less interesting stuff. But if this *still* doesn't sound like enough
for you, we have yet another option - while the free file share is
restricted to Gold accounts for obvious reasons, we're making Bungie
Pro available for purchase for your Silver accounts as well. You've
created "mule" accounts in an MMO, right? Betcha never guessed you'd
get to do it in Halo, too!
But wait, there's more! (That's me saying "But wait!" this time, not
you.) Browsing file shares in-game is one way to find content, but it
can get a little cumbersome. That's where Bungie.net comes in. When you
visit the website, you'll be able to look at your file share, and
everyone else's as well. Saved films and variants, of course, aren't
viewable on the PC because they're just a sequence of game data, but
you'll be able to pass around links, see the file descriptions, and
even click a button to add it to your download queue - next time you
sign in to Halo 3, the game will auto-download the files (up to 8,
currently) that you selected on the website. Screenshots, though, you
can view directly on Bungie.net and save off as wallpaper -- and they
look *great*! Add to that features like "copy to my share" where you
can import a file you like on someone else's share directly to your
space (or your mule's) so you and your friends can find it in-game,
file ratings, and discussions, and we think you'll find this to be an
essential part of the Halo 3 online experience."