Mash efficiency measures the gravity and volume into the boiler at the start of the boil, i.e. how well you got the sugars out of the grain.
Brewhouse efficiency measures the gravity and volume into the fermenter.
I spend quite a while confused as to what these numbers were and what I should be using in recipe planning software such as BrewMate.
Recipe planning software typically has you set your efficiency at (for example) 75%, set your brewlength (23 litres), and has you enter your grains. It then calculates your OG for you.
But this (at least in the software I've used) isn't affected by the hops you specify, or the deadspace in the boiler, or the length of boil and rate of evaporation. The brewlength isn't the volume you want in the fermenter, it's the volume you want in the boiler after cooling, and I hadn't realised this so I kept plugging in the volume I wanted in the fermenter.
I was finding that with a hoppy beer I'd end up with lower volume into the fermenter than I wanted, but maybe at the same gravity, and this certainly wouldn't be the 75% efficiency. If it was a shorter brewlength I'd also be out, as the deadspace would make up a bigger percentage, since it's a constant volume.
These days when I use recipe planning software I set my efficiency at 75% and formulate the recipe for the gravity and volume I want in the boiler at the end (26 litres, say), guesstimating 3 litres of loss to the hops and my boiler's deadspace, a little more if it's a very hoppy recipe, so I end up with the right sort of volume into the fermenter (23 litres).
Everything now seems to work out as I expect; I get both volume and gravity about as planned at the end of the boil, and the only variation is a minor one of the volume into the fermenter.
Or am I still confused? ;-)