Recently I've been playing the Queen's Gambit Declined as my primary response to a d4 opening by white. While analyzing past games with engines, I've realized that as the game progresses, there's a point when suddenly whoever plays cxd5 and dxc4 gets a huge advantage. For example, maybe there's position rated -0.6, then it becomes -1.1 on black's turn recommending the pawn exchange, and if black doesn't play it, it suddenly becomes +0.2 for white to take the pawn.
This advantage is seemingly more valuable than developing pieces and seems to drastically change the position. Though it is is important to note the white fianchettoed their bishop on g2, making the position similar to the Catalan, noted by Alexander Woo in the comments section.
Something else I noticed about the position is that if black loses their d pawn, the engine doesn't really care, but if white loses their c pawn, the engine's rating of the position drops from -0.2 to -0.8.
It seems that somehow, before a point in the game, playing this exchange is highly unfavorable, but at a random moment, it becomes very favorable, such as when I develop my queenside knight in any way, the engine suddenly recommends the pawn exchange, which doesn't seem like it does anything.
Could someone who is experienced with or knows a bit of theory please explain to me when this move should be played, its purpose, and its effect? I've checked a few online guides but they only talk about the early moves in the opening and none really elaborate on the purpose and timing for the pawn exchange here.
[Here](https://lichess.org/8PIQ8KUh/black is an example game I played of what I'm talking about.
Please ignore my horrible attempt of a kingside attack but the engine starts fixating on the pawn exchange for either side at move 6 for both white and black.