They're a large, mostly well-behaved grid load which lets you spread fixed costs over more units of electricity.

The problems start when they are being built by well connected entities that can leverage their power to simply demand that other people pay more to give them a discount.

Very similar to the shopping around factories do. Usually a factory brings jobs and other good stuff, but you don't get the factory unless you do X, Y and Z in competition with all the other possible locations. That can lead to a winners curse where you're effectively subsidizing the factory and losing out overall if you "win" the auction.

Scotland's abundant local energy resources should be spent on things that actually benefit Scotland and provide jobs.