I try to let BeerSmith do the heavy lifting as much as possible. I called and got the mineral content of our tap water and entered that into the water profile database. Then I create a profile for each basic style I brew. Example: "Local" = our basic local tap water. "Local-Pale" = Additions to" Local" to brew pale ale. These changes are pretty much taken from John Palmer's suggestions.
When I brew, I have limited kettle space so I start with 12 gallon of say "Local-Pale". I let BeerSmith enter the required additions to my Recipe Ingredients.
I'll use say, 7 gallons in the Mash. I will sparge with 9 gallons. So after I put the strike water in the MLT I only have 5 gallons of treated water left in the Kettle.
To get my 9 gallons to sparge, I'll need 4 gallons of water more in the kettle. So in the Recipe Ingredients, I make another Water entry of 4 gallons. I let BeerSmith show the additions I need to put in the kettle to correct the 4 added gallons. That way I mash and sparge with the same water profile.
The Mash Tab tells you the water volume for the mash and the sparge.
In practice I heat the initial 12 treated gallons up to strike temp. After I strike, while the mash time is running, I add the 4 gallons and treatments to get the volume of sparge water and heat it to my sparge temp. I should add that I batch sparge rather than fly sparge to a gravity value. This keeps my water volumes easy to calculate and treat.
Here's my confession, by using this method, I pay absolutely no attention to the" Use During"! It isn't used in any calculations that I make or use.
Pat