Photo Source: Summerhill

Photo Source: Summerhill

Photo Source: Summerhill

Using batts in a wall cavity with electrical boxes:

The batt needs to be cut at the same height, and in the same place that the electrical box will be located. If the batt is not cut and placed around the electrical box then the batt will be compressed and be less effective in the wall cavity. It could also leave gaps of uninsulated areas short circuiting the insulation.