You hold your breath as the screen loads. Then you're back where you were moments before, quest objectives flanking you on all sides, and so far it looks like no one from the group has noticed your disappearing act. You knock out a few more quests, all the while eyeing your chat frame with the hope you won't be discovered. The first boss falls. The group wipes on the second boss, but quickly recovers and is onto the third. By this time, thirty minutes have passed. The third boss is more challenging than the second, but after a few wipes, some rage quitting and reforming, the third boss dies and the group heads towards to fourth.
Aware of the raid's progress the entire time, you right-click the little green eyeball and choose "Teleport to Dungeon." You port into the instance and join your fellow players in front of the final boss. The fight goes down without a hitch and when the boss falls the RNG gods curse you for abusing the system and you get no loot. Ever again.
But no, really, you may end up getting loot, but that's beside the point. You shouldn't be acting like the player above in the first place.
My Time is Better Than YoursSee, that player has determined that his/her time is significantly more valuable than that of the other 24 players in the group. They desire the ends, but don't wish to bother with the means of achieving those ends---even when they've essentially pledged to do so by entering the queue with 24 others in the first place. The LFR Parasite takes advantage of a flaw in the system that results in the exploit of their fellow players for personal gain. The LFR Parasite wins regardless---they don't "waste" their own time while reaping the benefits of a group they've latched onto. Worst-case scenario is their ruse gets discovered and they get voted from the group. Only to queue up again.
The LFR Parasite can be found in many forms in addition to the one described above. Other common variations include the Auto-Follow Parasite and the DPS-Queues-As-Heals Parasite. In all of these cases, the Parasite desires a reward that's only achievable with a group but doesn't wish to contribute effort of their own. "Well that's just another term for a 'carry'." No, it's not. The Carry may be there for a variety of reasons, while the Parasite involves specific intent to abuse the power of the group.
But what harm does it really do if one person decides to game the system in this way? The short answer is not much. LFR, by design, isn't tuned for 25 players at the top of their game. Anyone who's defeated the bulk of the Durumu encounter with seven people alive can attest to this. In other words, the absence of one person won't make or break the chances for the group's success in most cases. But what if three people did it? Five? Seven? Sooner or later, the impact will be felt and math alone dictates the percentage chance of the group's success will eventually plummet to zero.
It's not so much the action itself I take issue with, but the attitude behind that action, which I feel is a symptom of something much larger that permeates the MMOsphere: a blatant, callous disregard for how one's own actions could negatively affect fellow players. Heck, it's this disregard that really led to the idea for Don't Be That Player.
So you don't act like an LFR Parasite simply because it's not nice or considerate of your fellow players. I know when I enter an LFR that most players won't be dishing out top-tier DPS, but I do assume that if they're there, they'll at least try---after all, that is the purpose LFR: to participate challenging encounters with other players. If you're worried about the value of your own time in-game to the point you'll outright play the system to exploit other players, you're doing it wrong.