[Bongle]

A bit more off-beat answer is city planners. The GIS software that they use to analyze spatial data requires good knowledge of set theory in order to deduce results.

For example:
Task: Find a suitable site for a new daycare
1. Select all sites in the right zone code.
2. Remove all sites that are within 1000m of a jail
3. Remove all shapes that aren't compact (perimeter / sqrt(area) > 6.0ish)
4. Remove sites that aren't near major roads
... many more steps of elimination ...
5. You will almost certainly end up with several sites that meet all your "hard" criteria like law and bylaw-compliance, so determine a weighting of the attributes of the remaining sites so that you can create a ranking of which sites are best. For instance, one site may require upgrades to the existing building, while another may require the design and construction of a new building. Depending on what your priorities are, one may be preferable to another.

I think though, this is another job where math skills aren't NEEDED, but they certainly help your thinking a lot.