although I personally think that "ASSUMING CONTROL" should've made it in there every time something gets possessed...
How many times a match does something get possessed? How many times a second on late-wave gold/platinum matches? Were you here when Reave never stopped?
Absolutely. First time a Collector is possessed per wave would be more than enough, even if it's one of two dozen different quotes. There's plenty of ways to implement Harbinger's voice without it becoming that repetitive.
Having Harbinger focus his attention on a bunch of random operatives makes no sense lore-wise. The Reaper leading the charge on the galaxy has bigger fish to fry, e.g. Shepard.
The same could be pointed out as to how every Collector unit can be possessed. Is each one a single Reaper possession? Why would dozens of Reapers focus their attention on a group of operatives?
Who says reapers can't multi-task. One reaper controlling multiple collectors.
Personlly, I don't think it should be done on possessions at all. Like some others have suggested, it should be for more specific, and less common, occurances. Players getting downed, objectives, and maybe some randomly placed taunting, for example
There are 10 types of people in the world. Those that know binary, and those that don't. Gamertag: Talon Omega