When it comes to the interior of occupied homes or office spaces, we apply paint by brush and roller.  We are careful to properly cover floors and furniture to protect it from paint and sheet rock dust.  In a lot of industrial settings where there are wide open spaces we usually spray the walls and ceilings.  Warehouse spaces are a good example of that.

When painting exterior surfaces such as siding or exterior ceilings we customarily spray these types of surfaces.  All bushes and surfaces that could be affected by over-spray are covered with drop cloths.  Soffit surfaces are usually sprayed as well and shields are used to protect roofing.  Other trim such as windows, doors, and gutters are normally brushed.