When I carry, I get my defense, shielding, armor, and that's about it. Those stats are pretty unreliable when being focused by multiple people in PVP because so many abilities that players have bypass them (for example, everything that happens in ******* Operative openers).
When I am protecting a carrier instead, that person gets a flat 5% damage reduction from Guard, 50% of the damage they take is transferred to me, everyone around them does 4% less damage thanks to Combust from Flame Sweep, and on top of that I can taunt enemies who are focusing him for 30% less damage. Oil Slick is also actually useful for guarding people in warzones since it debuffs enemies instead of buffing me. Plus in an emergency the carrier can lateral the ball to me and I can usually hold out with my tank cooldowns until help arrives.
The problem with this bodyguard style of play is that when I queue alone I am forced to rely on someone else to be competent and want to win, traits that are apparently quite rare in random PVPers. Usually the groups I end up in just ignore the ball and teamfight across the map from it, leaving me to try to carry or stop their carrier alone. WHY CAN'T YOU JUST TARGET THEIR CARRIER! RRRRRRGH!
... *ahem* I think it's time for me to take a break.