In the dept. of poured-concrete construction, house-building 101 looks something like:
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. :-)
Peetie