I did full, or nearly full, volume mashes for about 2.5 years for BIAB'ing.
Well the main reason I switched was due to equipment constraints, I moved and left behind my big pots. I was doing .75-1.5G batches in a 2G pot. Coincidentally I had a 1G slow cooker which lined up perfectly with 1.7-2 qt/lb. Compounding this is that I have .5G boil off rate with the 2G pot, so with such small batches I get a substantial amount of malliard reactions and a higher than usual total water to grain ratio which would a no sparge mash thickness around 3 qt/lb.
Then I did a crap ton of reading on efficiencies and put in place the batch sparge / mash analysis section of my brewing/biab calculator and learned that the thinner mashes tended to have higher conversion efficiency (first running gravity and strike volume, aka extract converted and in the first runnings + retained wort).
For lauter, I (and braukaiser) define it as the extract produced by the combined gravity and volume for first and second runnings. For zero mash tun loss, mash = conversion * lauter.
Since I get high conversion efficiency, and high lauter efficiency due to a well done batch sparge, I have no intention of mashing full volume again unless I'm feeling extra lazy. Combined this gives me a high mash efficiency that I doubt I would be able to obtain for full volume mashing.
I have a predictable model thanks to braukaisers findings on batch sparge simulations, and doug293cz from HBT creating a simulation spreadsheet for BIAB.