While it first appears that black falls behind in
development, white will oftentimes have a difficult time exploiting this. While this may seem odd at first, because the black king looks very
exposed on the white bishop (open file leading into the king). Black is actually more than protected, and an eventual Qe8 for black will completely protect the light squares in the black camp.
If played correctly by black, black should be able to easily catch up in development (black will go behind in development after those first two pawn moves: 1 ... f5, 2 ... g6, at least in the Leningrad system) and will eventually gain a strong control over the center and kingside of the board. We can see with the generally accepted first moves of the Leningrad System,
1.d4 f5
2.g3 Nf6
3.Bg2 g6
4.Nf3 Bg7
5.0-0 0-0
6.c4 d6
7.Nc3 Qe8
8.d5 Na6
The plans of both parties. White will continue to expand on the queenside, and will pressure the weak point on e6. White will attempt to prove that e6, with no pawns defending it, will be a fatal weakness. Black will attempt to prevent this from happening with the move 8... Na6, which threatens to bring the knight to c5, protecting e6, and as we know, if a white pawn ends up anywhere near e6, a knight is the best blockader for such a pawn.
Meanwhile, Black's queen at e8 is in an ideal position to support g6 if the pawn at h7 decides to advance; or potentially, the queen could move to f7 and support nearly every piece on the kingside, as well as protect e6.
White, if possible should focus on gaining as much space as possible on the queenside, and eventually squeezing black to death. White should, and usually plans on simply stalling the black expansion on the kingside, and overloading the black queenside with pieces.
This opening is suitable for players who are having a "defensive-block" about what to play against d4. It is also very good for players who are interested in some interesting pawn structure and some very fun pawn endgames. I should warn people about that though, because even if black does go ahead by a bishop, the cramped pawn position will usually lead to a draw in the endgame. In fact, at the master level, 31.6% of games are drawn in the Dutch.
If you enjoy rapid expansion, and the entire concepts of expanding and attacking, drawing attention, and decoy's and are just a little familiar with chess tactics, then I would recommend using this opening. It offers a lot of freedom and creative outcomes.