The initial reconnaissance of the V'ger craft is yet another moment of loving effects work. Portions of it recall 2001 A Space Odyssey, particularly the cloud entry. Some portion's of V'ger's fore I swear I've seen recalled in more recent works such as Mass Effect.
The key trick of the entire part of the film is much like a stereotypical horror film axiom: "Don't show the entire monster -- at least at first". Films such as Pitch Black used this to great effect, but TMP also employs the same trick here.
Instead of instilling fear by withholding information, the purpose of the sequence is to impart a sense of awe and smallness in comparison. This is muted at first, until the entire Enterprise -- already a giant at human scale -- is shown. The V'ger craft takes up the entire screen, implying to even larger than our godlike cinematic gaze permits, while our favorite starship is a mere slot car in size. In the theatrical cut, our satisfaction is entirely denied in seeing all of V'ger at once until a brief frame or two prior to it's disappearance. The Director's Cut had CGI on its side, so we get delicious detailed shots as it approaches earth.
The original pan sequence took a significant amount of time to film. Shot frame by frame in a smoke filled set over the course of hours. If I recall, at least 12. This, no doubt placed extreme demands on the V'ger model. A full reveal may not have looked good with the technology of the time.
In a way, the earlier slow sequence of the Enterprise reveal parallels V'ger's reveal. The Enterprise sequence emphasizes wonder and a sense of majesty while also establishing a human scale for the ship. Star Trek has *never* been good at scale -- even as late as Voyager did such issues persist -- but it does give you a gut sense of it. Returning to the V'ger reveal, the sense of smallness and implied threat is amplified. If only the two sequences were closer together could the parallel have been made more strongly.
But *damn*, is the inside of V'ger pretty...