I don't know the significance of supposing that Oswald's visits to the embassy/consulate (or to Mexico) was faked. But I think that the speculation persists, in part, because the CIA was photographing people upon exit and entrance, yet failed (apparently, supposedly) to photograph Oswald.
Yet they did photograph this other person, whoever he is, and attempted to associate the photos with Oswald. It is an oddity.
When you're looking for evidence of a conspiracy or a cover-up, or to disprove the same, you have to probe such oddities. (Because, to the extent that a cover-up is successful, all that will be left are such apparent incongruities; the actual evidence is meant to be suppressed -- that's what it means to cover-up.) Why was this man's photo identified as Oswald? Why weren't there photos of the real man? There are claims that Oswald's phone conversations were recorded, so what became of the recordings?
Anthony Summers (who may or may not be reliable) quotes an FBI report as stating, re: Oswald's visit to the Soviet Embassy, "Special agents of this Bureau, who have conversed with Oswald in Dallas, Texas, have observed photographs of the individual referred to above and have listened to a recording of his voice. These Special Agents are of the opinion that the above-referred-to individual was not Lee Harvey Oswald." And then he goes on to quote J. Edgar Hoover in conversation with President Johnson, saying, "That picture and the tape do not correspond to this man's voice, nor to his appearance. In other words, it appears there was a second person who was at the Soviet Embassy down there."
There could be any number of reasons for these "oddities," including innocent error, but surely it's worthwhile to question them? I don't know that Kennedy was killed as a result of a conspiracy, though I highly suspect that he was; I don't know what role Oswald played, before, during or after the assassination. I do know that the CIA specifically got into all sorts of monkey business throughout the sixties and beyond. Their behavior with respect to Oswald's visit to Mexico is suspect at least, whatever it means for broader questions about the assassination, and I think it's worth investigating for that reason alone.