It is the grain bed temp, not the sparge temp that you want to monitor.
This is an important point.
The grain bed should reach 168F-170F during the sparge. So after the sacch. rest, one will need to infuse or rinse with water higher than the targeted temp in order to achieve those temps. Typically the strike temp will be 20-30 degrees higher than the target temp depending on the amount of grist, initial temp of grist and volume of water added. There are some decent brewing programs that will calculate this for you. I like Beersmith 2.
So there is where I am confused. I just heat my sparge water to 170F and use that. After recently listening to an episode of Brew Strong on sparging, John Palmer seemed to say that the sparge water (not the grain bed temp) is fine in the 170F to 175F range. In fact, he even suggested you could just use warm water and it wouldn't make much difference. When describing the original mash process he said nothing about doing a mash out in regards to the first runnings, and in How to Brew he states that many homebrewers skip this step and it doesn't negatively affect their beers. All this is a long way of saying that I don't do a mash out and I only heat my sparge water to 170F.
But, after reading a comment from Denny the other day who said he heats his sparge water up to 185F (or something along those lines) I was confused. So I looked into Denny's batch sparging tutorial. It makes reference to doing a mash out, but also makes reference to getting the grain bed to 165F to 168F during the sparging process, but doesn't really explain why. I understand a mash out is to stop enzymatic activity. But once that has been done, what is the benefit of raising the grain bed temp to 165F to 168F during *edit* sparging? I'm sorry for the very long winded question, but I want to understand as much as possible.