You begin play normally, but unlike the rest of the team, you spend as little karma as possible.  While everybody else is racking up skills, spells, and chrome, you spend cash but little else unless you really have to (it's not worth dying for to skip that spell that you knew in advance could save your hide).

Eventually, you build up to 87 karma.  This is where the fun begins.

You initiate, taking the Familiar ordeal to cut initiation costs and avoid having to take Ally Conjuration in advance.  You design a F9 Ally, with 1 form, 1 skill (Exotic Ranged Weapon, for elemental attacks), and 9 powers (little things, like Concealment/Movement/Guard/Elemental Attack).  Total cost, 77 (9x8+1x5) karma, plus 10 karma for the initiation after discount.

To create your Ally, you have to summon at 9 dice and bind at 18 dice, immediately.  This makes it a little dangerous, so get all of the dice that you can--healers, medkits, etc., and spend Edge like a drunken sailor.

But when all is said and done, for the cost of 3-4 Edge (spent, hopefully not burnt) and 87 karma, you will have a faithful best friend capable of scouting, sneaking your team around (and/or hauling tail), blocking glitches, and stunning/killing anybody in sight.

So what?  Any spirit can do that.  But your Ally can do it day and night, without orders, without any further binding.  And that's just the beginning.

Your Ally is going to stick around, so why not invest 4 karma on quickened Improved Reflexes?  Dirt cheap for the huge always-on increase in firepower.

Raise the force to 12 (48 karma), and start adding skills and spells, and you'll quickly gain a high-caliber medic, protector, face, wheelman (sans rigging), and sharpshooter (for those times when you don't want the opfor knowing you're packing mana).  We're talking 24 dice to any activity that your Ally has the skill for; and it costs only 5 karma.  Imagine walking away with a net of ~$200K/month making orichalcum.  In addition, while 18 hardened armor can be penetrated by a good sniper, 24 hardened armor is really, really tough to beat in combat.  The sky's the limit, but you'll want to save up your karma and do the re-bind as few times as possible, to reduce the risk of having to burn Edge on the Bind roll.  Powers scale with F, too; imagine being Levitated at upwards of 450m/turn while effectively invisible

Oh, and if you're nice to your Ally, and they are willing to pay the price, you can have them soak the drain from the re-bind.  It'll be (2xF)P DV for them, but they have a lot more drain dice and HP than you do.

Or, if you're masochistic, you can save 24 karma by waiting until you have at least 101 karma for the initial summoning, and start off at F12.  That's a little dangerous, though, especially since you have no Ally to soak the Bind drain for you.

Finally, you can always pump your Ally to F16 or even F20+, although this obviously requires several levels of initiation.  It also requires burning Edge to make the binding rolls most of the time, so never, ever do this until your Ally has all of the skills and spells that you ever expect them to need.