User blog comment:JakePT/Arrival has Arrived/@comment-1891865-20110330173914/@comment-1221773-20110331034138

Object Rho is probably exactly that, a beacon. Whatever else it may do, I think a core function is to guide the Reapers to the Alpha Relay in the event the usual route through the Citadel is closed off. The galaxy and stars don't stop moving when the Reapers hibernate, so it would make sense that they would need some way to get their bearings.

As for the continuity errors, I'm going to have to say that they can't be reasonably explained away. I don't think when you play Arrival is going to affect ME3 at all, but if you choose to play Arrival before the suicide mission, the price you pay is a greater effort to suspend disbelief in ME2.