When should white take on d5 in QGD, slav/semi slav structures?

When I play d4, c4 as white I don't generally take on d5 if my opponent doesn't chose to take, and keep the tension in the centre. I see some lines in the opening explorer where white takes on d5 after development, or even before. In what cases and for what reasons is it beneficial to take the pawn on d5, and how are these lines different when u dont take on d5?

If black plays ... b6 in order to play Bb7, then cxd5 is sometimes worth playing to fix a black pawn on d5 and render ... Bb7 pointless. If you wait until black has played ... Bb7, the long diagonal may open with a knight recapture.

d4 c4 openings started to make sense for me when I learned about the carlsbad structure. I remember especially the concept of minority attack being an eye opener. Check that out if you haven't already.

www.youtube.com/watch?v=qfy86Wm1Waw

This might help you, it has sections on slav and queens gambit structures. It has detailed discussion of different pawn structures including what your goals/plans are in these structures, and includes discussion of when to be pushing pawns amongst other things. I don't pretend to be of a level where I can critique the info in there or anything, but it was provided to me by another high level user @tartakowerck , and I've gained a lot of knowledge from it so far (though putting that knowledge into practice is another thing altogether!).

simplifychess.com/pawn-structures/complete-guide-chess-pawn-structures/index.html