no matter what the profile of the rest of my recipe, the sparge water temperature is always 168 degrees. Why is this? I've been advised, and used to good effect, the technique of setting the mash profile instead to mash in/mash out, and using the mash out temperature for my sparge water. But that seems unnecessarily complicated when I'm not actually mashing out.
For everyone's sake, let's define both parts to the lautering/sparging process.
The hotter the sparge water the better it will rinse the sugars from the grains, however, sparge water is usually always cited at 168F to 170F because at 170F the tannins and other nasties in the grain husks become soluble enough to be rinsed into the wort. Apparently this is more likely with sparge water pH above 6.0. And for continuous sparging, most texts recommend stopping when the runnings measure 1.010 or maybe 1.008. After that point, risk of tannins increases again.
Separately, to make lautering more efficient, the "mash-out" step follows the mash, and means the brewer takes the mash temp from whatever (i.e., 152F) up to 168F, either with hot water or direct heat. The benefits of a mash-out include efficiency, b/c now the entire grain bed is 168F, as well as the sparge water, so sugars rinse more easily.
If I understood your question, you're asking how/why to set the sparge water temp to whatever you mashed at?