When you consider a pawn exchange, you should evaluate the impact it will have on the position, and on both sides' game plans respectively, because they are connected with the pawn structure. In a position there can be pawn exchanges that favor you and ones that favor your opponent. For examle, a pawn that attacks (and in this way controls pieces' access to) a certain square can be useful to its owner and an obstacle to the opponent. Also, if you need to attack with a rook along a file, you may want to exchange your pawn on that file to increase your rook's scope, or to move or exchange a pawn to open a diagonal for a bishop, and so on.
A pawn advance that threatens to exchange the pawn moved and result in a more favorable pawn structure for its owner is called a pawn break. You should play your breaks and prevent your opponent from playing his.
In the game you posted, White played very passively in the opening, and after 7.c3 you've already developed all of your minor pieces, and your opponent has developed only two and has blocked the other two in such a way they'll require him to spend time to just get them into play:
You then play ...e5 and ...e4 (even if White had exchanged 11.dxe5 you still stand better because you are ahead in development and center control) and you get a position where you can attack White's kingside along the b8-h2, c8-h3 and d8-h4 diagonals, you've got pawn control over the c3 hole, White is weak on light kingside squares, his knight is inactive and vulnerable to g7-g5 on h4, and his queenside pieces are cut apart from defending their kingside because of the closed center and your d5-e4 pawn chain that denies them access to c3, d3 and c4:
In other words, you have a strategically won game, and should the pawn structure remain the same, you have a win with correct play. Hence White needs to change the pawn structure to get some defensive possibilities and/or seek counterplay, and try to exchange his pieces for your ones that are more active. Since White's major problem with the pawn structure is the d5-e4 chain, he should seek ways to exchange those pawns, with the best one being the preparation of c3-c4 and dxc4 (afterwards e4 is vulnerable) and then using the gained queenside space and lines opened.
That's why 12...Qe6 is a mistake (you had 12...Bg4/12...Be6/12...Bd7/12...Bc8 keeping your bishop in the attack, with Black retaining a strong advantage). White then has Nxf4 and c3-c4 and has an equal game. He missed 15.cxd5 though, but you in turn missed 15...Bg4 (16.dxc4 will lead to 16...dxc4 with Black keeping his advantage) keeping your bishop in play, and played 15...dxc4 instead which gives back equality to White.
This game is an example of how much a pawn trade can influence the game (White's c3-c4), how important it is to coordinate your pieces and pawns (compare White's opening with your development and early middlegame play), and how to exchange pieces that are not active due to the pawn structure for active ones (16.Nxf5). That's why it's very important to be able to analyze the pawn structure and its influence on the game, and if necessary to modify it as quickly as you can (11...e4! immediately after White missed 11.dxe4; 13.c4! immediately after 12.Qe6) while preventing your opponent from doing so.
I have encountered many games where either I or my opponent must take pawns in the center to be able to do anything, but is it better to wait it out, or to iniate the trade? ex:
Any input will be apreciated, and thank you to those who consider this and help.