In the dept. of poured-concrete construction, house-building 101 looks
1.) Dig large rectangular hole in ground.
2.) Set concrete forms.
3.) Pour footings.
4.) Lay drain pipes, etc
5.) Pour foundation walls.
6.) Pour Basement Floor.
The BF conforms to the shape of the ground at the time poured.
20-60 years later, the ground under the BF might have shifted, and
not necessarily uniformly. So the owner, given water problems in the
basement, considers "waterproofing" the bsmt. with French Drain system
and sump pump(s).
If FD system is initiated, what guarantees that the BF will not
shift/tilt when they knock off the concrete around the perimeter
of the BF, such that what's left of the BF is no longer sitting
on the footings? Keep in mind that there's no way to know exactly
how the footings were constructed before beginning the work.
Inquiring minds floggin' well ask potentially dumb questions sometimes. :-)