[Gibbon1]

Two things.

Lot of reactions are energetically favorable. But the reactants are stuck in a local minima. So either doesn't happen or is too slow. Enzymes mediate the reaction so it can happen or happen faster.

Lot of reactions there are side reactions that produce stuff you don't want. Resulting a terrible yield or maybe none. Enzymes can promote the reaction you want increasing the yield.

Interesting thing to watch for is eletrocatalysts. Where you use electricity and a catalist to push a reaction that is energetically unfavorable. Like CO2 + H2O --> methanol. These may become very important as we stop pumping oil and gas out of the ground.