Piece up, queen trade or not?

You are a piece up. Do you want to trade queens or not, generally speaking?

Yes, of course.
If you are up material, trade pieces, not pawns.
If you are down material, trade pawns, not pieces.

Yes, typically you want to trade pieces to simplify into a winning endgame when you have more material. When you have less material, you typically want to avoid trading pieces and you want to complicate the position if possible; this will give them more chances to blow their advantage.

Unless you can see a clear way to use your Queen to win material or Checkmate first then forcing a Queen exchange will make your win more likely. Your opponent should try to drag you into complexity and should try to simplify.

Normally I trade down to simplify the position and minimise the chances of a counterattack. After all, once the queens are off the board, I feel safer with moving my king forward.

This is, however, less true as the endgame phase approaches.