If the material is massive it doesn't matter much. But if it's just a pawn, that's almost always not the case. Having an extra pawn means almost nothing if your activity is poor.
Exchanging when up material to the point where you're obviously winning, but not to the point where your opponent is only embarrassing themselves by not resigning, should typically be saved for occasions where your king is under heavy fire. In particular, getting the enemy queen off the board should be a top priority.
Other than that, you should probably try to gain other advantages as well before trading down.
I'm not sure if this is the right place to ask this question. Let me know if I should post it somewhere else.
In the recent match analysis by @GM_Bondo3, which won for best analysis in February, he has a rule that you should always trade when up in material. Is this correct? What if you are up a pawn and you can trade an active bishop for your opponent's knight, which is on the edge of the board? Should you trade since you are up material, or should you avoid the trade since the knight is seemingly weak?
You can see GM_Bondo3's analysis here:
https://www.chess.com/a/35rNkQqmpECsG/analysis?move=41