No, not planning permission for the shed, planning permission for running a business from home.
If he is running a business from home, and bringing the public into/onto the proberty, in this case a garden shed, then there are a few things that should be considered.
1. The insurance aspect, if they have an accident/trip/fall (or get electrocuted) then is he/are you covered
2. Running power to a shed that is running as a business would necessitate all the releavant certification from an electrician, otherwise you could well fall foul of 1 above
3. Planning permission would be required for using a shed as a business, especially one that involves the public (as opposed to a workshop for instance)
It's all very well to wing it and run an extension out to the shed, but if anything happens, you could land in a world of problems.