The only efficiency I care about is conversion efficiency, how well you're converting the starches in the grain into sugars. Everything else is just volume losses.
Each grain has a gravity points possible per gallon of water (PPG). 2-row has a PPG of around 37. This means at 100% efficiency, you would get 1 gallon of 1.037 SG wort. If you did 2 gallons it would be 1.0185 SG. If your efficiency is 80% you would get 1 gallon of 1.0296 SG wort.
To get your conversion efficiency you just need to measure the post-mash volume and SG (after squeezing the bag), and know the weight and type of grains.
Brewhouse efficiency includes volume losses which I find to be more confusing as a measure of efficiency. So I just estimate those directly as volume losses.
I suppose this is one way of looking at it, only relevant to BIAB or other no-sparge brewing (yes, I know this is in the BIAB section). But I do agree with with disregarding brewhouse efficiency as a general figure. Some factors, like the protein content of the malts you use, or the hop bill, or procedural things like whether or not you whirlpool/rack off trub/whatever, or what chiller you use, will dramatically impact brewhouse efficiency and resulting fermenter volume, but don't actually impact the gravity of your wort, and will often change recipe to recipe (especially with hop losses).
I think in terms of conversion efficiency and overall "mash" efficiency, which would more accurately be lautering efficiency.
Conversion efficiency- how effectively you transform starch into sugar and release it into the wort
Lautering (or mash) efficiency- how effectively you get that sugar into the boil kettle
Brewhouse efficiency- how effectively you get sugar AND volume into the fermenter.
The top two can be very rigorously controlled and consistent. If you follow proper mash procedure, you can reasonably expect to hit 98-99% conversion efficiency absolutely every time you mash. With proper equipment setup you can dial in your process to hit the same efficiency every time, or close to it (there's a necessitated change when water to grain ratios change, effectively higher gravity beers will see lower efficiency and lower gravity beers higher efficiency, but if the water to grain ratio stays the same both in mash and sparge, and the boil lengthened or shortened to compensate, you would expect exactly the same efficiency).
I mention the "IF" part about BeerSmith and equipment because if you allow it to design a recipe based on brewhouse efficiency, but your losses aren't factored in correctly, it does weird things. I prefer to zero out ALL equipment losses, have the software treat mash efficiency and brewhouse efficiency as the same thing, and factor the losses in my head.
As indicated above. To bring it full circle.