What’s the pros and cons of using the Indian Defense move order for the queens gambit declined.

What are the pros and cons to using the Indian Defense move order for the QGD? Like 1. d4 Nf6 2. c4 e6 3. Nc3 d5

In general the biggest con of 1. Nf6, as far as sidelines go, is probably you have to face the Trompowsky instead of the Levitsky attack. Biggest pro for a below-master player who's looking for just one solid line... is probably that there are some stronger c5/Qb6 lines against the London, even one leading to a forced draw.

As for the range of main defenses they lead into (flexibility is one factor for consideration) - the slav / QGA are better reached via 1. d5, and obviously the KID / Grunfeld / benko / nimzo indian / QID are only reachable via Nf6. The slav / QGA are more fighting openings, the KID / Grunfeld / Nimzo indian / QID are more positional and theoretical.

Just for how they deal with sidelines I'd probably lean toward playing Nf6 over d5 simply because I find the london very boring, and if I can spice that up or shut it down... I'm willing to play the Trompowsky to achieve that. And there are some cool lines against the Trompowsky, I like the c5/Qb6 variations there too.

For a QGD player it's also better to play Nf6 - this has the additional benefit of pressuring your opponent to play the anti-nimzo setup, which leads to a sub-optimal QGD exchange.

As mentioned already, con would be the Trompowsky. Another is the Catalan can be played without an early Nf3. 1.d4 Nf6 2.c4 e6 3.g3 whereas 1.d4 d5 2.c4 e6 3.g3 allows 3...f5, so typically the Catalan players will play 3.Nf3 Nf6 and only then 4.g3. 3.Nf3 f5?? Is bad because of 4.Nc3 Nf6 5.Bf4! followed by 6.e3 and 7.Bd3 with the ideal setup against the Stonewall. That is why Stonewall players must wait for g3.

One pro is some hate the Nimzo enough that they will play 3.Nf3 if they are not Catalan players. This avoids exchange lines with Nge2. Many nimzo players play the QGD instead of QID or BID against 3.Nf3 and they will go Nimzo against 3.Nc3.

I agree with the prev comments but there is one more thing I would like to add. One important feat of the Nf6 move order is that you can play a queens gambit declined and fully rely on the semi tarrasch defence. If white wants to play the exchange QGD without allowing the semi tarrasch, he can commit to an early Nf3 and this way allow the semi-tarrasch like this:

I'm really not following the logic in your post there. The move 3 setup where you have d5/e6/Nf6 with either Nf3 or Nc3 - that's reached from both the indian and the queens pawn line. It's the move 1 / 2 sidelines that will differ between Nf6 vs. d5 for a QGD player. Nf3 is played slightly more often against 1... Nf6, that's true, but that's just a slight probability difference due to psychological pressure, there's no material difference.

What I am saying is that by playing the Nf6 move order, black can choose to enter the QGD depending on what white does. If he for example do not like to play against the early Nf3 QGD for any reason, he does not have to enter a QGD. If you enjoy playing ALL QGD lines with black, well then there really is no reason to play Nf6 as it allows more sidelines like trompowsky as you mentioned. If you like playing against the Nf3 QGD and not the Nc3 QGD, then go for the Nf6 move order instead, where you dont need to transpose into a QGD against Nc3.

Practically the only serious reason is to avoid the exchange variation of the QGD by throwing in the Nimzoindian. If you feel comfortable in the exchange variation, then go 1...d5.

The most important drawback of 1.d4 d5 2.c4 e6 3.g3 is 3...dxc4 followed by ...c5, ...Nc6 etc. The omission of the move Nf6 allows Black to equalize quite easily.

Okay... but that's also true for 1... d5, you could play a triangle slav or QGA or something else. I'm still not really following the logic. What do you suggest black play against Nc3 after 1... Nf6 to avoid the QGD?

Some players who like the Semi-Tarrasch prefer to play 1...Nf6 and play the Nimzo against 3...Nc3 and go for ...d5 if White plays 3.Nf3. This helps to avoid Semi-Tarrasch lines with 7.Rb1 and 7.a3 which score well for White.