Most people want to put additions to their house. These additions may be in the shape of a second story over an existing floor or they may be an addition at the back or front with some load acting on the existing house.
The existing footings of the house are designed for the loads already imposed on them. Thus the existing footings have to be checked for additional loads.
It is important that the existing footings be checked before drawings are submitted to the county. All the counties are particular about the new loads. The plans will be rejected and precious time wasted if required checking is not done on the existing footings.