Cheaping out on electricity

I had some chips repaired on my windscreen at the Sandton branch. It was great, staff were friendly and helpful. Got the job done nicely. But I don't understand why the person carrying out the repair work had to plug into my car to power their generator for their tools, when I had driven to the PG Glass workshop? It's understandable if PG Glass comes to you. Surely PG Glass has their own electricity to carry out their work.