Why is compartmentalization in eukaryotic cells important?
concentration of reactants, organization
Every part of the cell is trying to use as little energy as possible and to also not waste anything, so releasing a bunch of calcium or glucose or whatever and making sure it goes directly to where it needs to go is crucial. Especially since reactions tend to piggyback off each other. You also want the right amount to be there to start the reaction and not to accidentally get involved in another reaction.