A lot of people commenting here are ignoring a key fact - measuring the gravity of the mash wort should be the #1 factor of how much water is being used. Yes, you need a baseline to start off at, so whether you use a calculator or use the 1.5 qt/lb ratio as your starting point is subjective. To that argument, if you are at your gravity, do you need to sparge? No, of course not. And by doing so, you lower your gravity. Most of the time you are going to be low, not high, and adding sparge water is going to make it worse. The mash process teaches you what your real efficiency is and how to hit your gravity from grain on a consistent basis.
None of the above, matters for a partial mash brew. The whole point of partial mash is that you are trying to get some natural sugars, and more important, flavors and aroma from actual grains. The majority of your sugars is going to come from extracts. So a sparge isn't needed for partial mash, because you are not looking to get every last bit of sugar from your grain in order to hit your gravity.
At most you may get half a point of gravity from a sparge. Typically it isn't worth it, which is why a lot of people do a recirculating mash process which negates the need, while gaining more efficiency.
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