Conditioner, dryer sheets, and similar products do what they do because there is some form of petroleum in them. The reason some fabrics "splotch" is because they have polyester in the fiber content. Poly is a fabulous fiber for textile manufacturers to work with because they can spin it to resemble silk on one extreme and on the other they can "shred" it to resemble wool. It is the later format that is found in sweatshirts, "flannel" shirts, etc. They have the barbs much like natural wool that mats together. This is why the conditioner will release the shrinking. The splotches come from the new petroleum products interacting.
To avoid those splotches as much as possible don't toss a dryer sheet in with permanent press. And if you have a lot of sweatshirts with high poly content wash them separately from similar items and again skip the dryer sheet.
Deb