The answers to this depend quite heavily on the move black played...
Pros and cons of 2. c4 vs 2. Nf3 after 1. d4
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Oh, right. I meant after 1... d5.
The main thing white avoids is the Albin Counter Gambit, 1.d4 d5 2.c4 e5 which should be OK for white, but is rather annoying (and dangerous!) in practice.
White might be going for a London or so, but those are not that strong and usually c4 will quickly follow anyway. But this means black will have to choose a move that they'd like to have played in both cases, and white can choose what to do based on black's reply.
The thing is mainly that if you play lines that involve an early Nf3 against all the 1.d4 d5 defences anyway, there's hardly any harm in playing 2.Nf3 and 3.c4 compared to the reverse.
It's mostly about transpositions.
After 1. d4 d5 2. c4 e6 White can play the exchange variation of the QGD and, after more development, play f3 with the idea of expanding in the center with e4. If White had played 2. Nf3 this would not be possible.
I play the Slav against 1. d4 (1...d5 2. c4 c6) and sometimes White will try to play 3. Nc3 and 4. e3, which results in different positions than when White has his knight on f3.
There are probably a few points in favor of 2. Nf3, but waiting to develop the g1 knight allows White to have the option of Nge2. It all depends on what you want to play.
The question comes down to whether you are playing c4 at all. If you intend to play c4 on move 3 it is usually a rather pointless transposition (unless black tries a reverse queen's gambit, see below).
1. d4 d5 2. Nf3 in my book usually means white is not going c4. If white wants to go c4, 2. c4 is perfectly good and I can't think of any benefit of a delayed c4. Black does some normal move and then white goes 3. c4 which is just a normal transposition and what is the point of that?
With 2. Nf3 White can then do a colle system/london system sort of thing and concede equality for the most part.
Note while 2. Nf3 does avoid the Albin Counter Gambit (rather rare in the first place), but actually can introduce other even more funky lines, such as 1. d4 d5 2. Nf3 c5!?, the Zukertort Opening, Reversed Queen's Gambit (D02). According to the database the only good move for white is 3. c4, which if black plays 3..e6 is a rather weird "Pseudo-Tarrasch" (Nf3 instead of Nc3). Don't ask me about 3..cxd4 or 3..dxc4 though as I have no idea.
What is a player looking for or trying to avoid with 2. Nf3?