Electricity cables running visibly through the house are not beautiful. When you have the chance, it is, therefore, better to have the electrics routed. It is a tough job to do yourself. A professional electrician has more experience and will therefore finish the job faster.
Before you start trenching in a brick wall, it is useful to have a good plan. Draw on a piece of paper how and where the electricity cables should run.
Tip: make sure that recessed cables only run vertically and directly above the wall socket or switch. This is important so that you don't know where you can or can't drill into the wall to hang a picture or mirror, for example.
When there is a clear electrical plan on paper, the electrician will mark out the cables on the wall. He will mark the places where the sockets should be.
Then it's time for the real work. Holes are drilled where the socket outlets are to be installed, with the socket outlets disappearing neatly into the holes. Then it's time to cut the trenches. You can carve out the slots with a chisel. But a professional will choose to use an electric trench cutter. That works much more accurately and quickly.
Because a lot of dust is released when milling, it is advisable to seal off the rest of the house!