Brew House Efficiency (BHE) is the amount of sugars from the grist which makes it into the fermenter. In BeerSmith, the BHE estimate in your equipment profile controls your gravity at the end of the process. It is affected by volume losses in the mash tun and throughout the process.
If your process is consistent and your losses always around the same volumes, then for the majority of your recipes the BHE will be reasonably consistent. When you brew higher gravity recipes, it may drop off a bit as the mash efficiency is slightly lower with a high grist to water loading.
Most people run consistently between around 70% and 80% for BHE and if your process is unknown (like the first time you brew on your Braumeister) usually a target of around 75% will be a good starting place and get you fairly close to the targets. From your first brew, if you fill in the readings on the 'session' tab BeerSmith will give you a calculated value for BHE as compared to the estimated value in your equipment profile. This can be found on the session tab underneath the column labeled 'Brewhouse Efficiency'. You can use these figures to help dial in your equipment profile. I would recommend keeping a record at first and using a running average to adjust the BHE in your equipment profile until you get settled in and are achieving fairly predictable results.