Turndown for a Post-Tension Concrete Court

my father has a sports court construction business and I work with him infield and in the office. He usually almost always builds the sports courts using post-tension concrete with 4000 PSI concrete. He also includes turndowns in all the courts he builds. My question to this would be: Is it necessary or beneficial to use a turndown for the slab? The reason he uses post-tension is to avoid cracks which really does work marvelously, but is it necessary to have a turndown when there is no load on the edges of the slab? Can it actually be a negative component of such type of slab since if there is some type of soil erosion on the edges of the slab where the turndown is, this will cause an uneven load distribution of the slab itself on the edges, even though they’re tensioned by the PT cables? Or is a turndown the right thing to do in this case? I’m not a civil engineer or anything but wanted to know if anyone had any insight on what would be best in this situation. Thank you!