Local implications and economic impact of datacenters?

Most datacenters are a pretty good construction project, but afterwards staffing is minimal. They can use a lot of power, so it's nice to have it sited near a generator project. Depending on who runs it, datacenters can be dispatchable loads --- if the grid has low supply, they can ask the DC to shed load. If it's a single tenant DC, they'll be able to move traffic to other regions; if it's a cloudy DC, they'll be able to restrict services and push customers into other facilities; if it's a traditional colo with lots of individually managed machines owned by customers, it might not be very dispatchable, but they could tranfer the load to onsite backup generators.

I've hear, when IBM build dc's in Europe, they use heat from dc to heat public pools.

Plus, currently ~1 admin for each 100 computers, will spend part of his compensation in near restaurants. Plus, onsite autos, most probably, will use nearest service.

That's near all impact. I have worked very close to dc's (my company have own server at dc), so few periods, I spent lot of time in dc and seen all typical operations.