Usefulness of SG reading on first, second, third runnings in batch sparge

I now have 3 batch sparged all grain brews under my belt. All were for 5 gallons of beer. Here is brief summary of my methods:

-All calculations in Beersmith2
-Add strike water from HLT via march pump to MLT (Large coleman xtreme cooler, maybe too large for 5 gallons)
-Stir in grain, and let sit for 5 minutes
-Take temp to see if I meet strike temp, if not add boiling water from stove
-Continue to monitor temp for 60, adding boiling water if dropping below 145F
-Voulauf by recirculating wort in MLT via march pump until clear
-Lauter 1st runnings into Boil Kettle via pump
-First batch sparge, stir, vorlauf, and lauter into BK via pump
-Second batch sparge, stir, vorlouf, and lauter into BK via pump

Over the course of these 3 brew sessions I've been trying to dial in on my equipment variables for use with Beersmith2. VOLUMES were my biggest problem, especially since it took me 3 batches to get my strike temperature and mash temp high enough and stable for 60 minutes (needed to add boiling water more than I wanted).

My third brew session was on point. My question now: what is the usefulness of taking an SG reading on the first, second, and third runnings? I understand that they should be decreasing in SG, but how can I use these numbers on the fly to benefit my brewing? I've been monitoring these numbers somewhat, but I don't quite understand how I can "use" them in the moment of brewing.

I'm also taking the pre-boil gravity after ALL runnings are in the BK. At least with this number I have an estimated number from Beersmith to compare, and I can add water or boil longer in the BK to compensate.

Thanks
DMC

You can use them to calculate efficiency. Kaiser's batch sparging efficiency spreadsheet needs OG and volume of every run-off to calculate efficiency.

Efficiency-Troubleshooting-Spreadsheet (under Calculating Efficiency):
http://www.braukaiser.com/wiki/index.php?title=Troubleshooting_Brewhouse_Efficiency