One of the primary motivations in developing the BglBricks standard was to facilitate the construction of fusion proteins. The underlying principle here is that proteins tend to fold in modular units called "domains". Some proteins are composed of a single domain, while others contain multiple domains. These folding units are often also functional units, and it often it is possible to recombine two such functional units from different sources into a single molecule and preserve the activity of both functional units. To explain this further, let's take a look at an example. Shown below is the crystal structure of an IgG protein and below that is a simplified representation of the IgG protein. IgG proteins are one of several forms of antibodies that are made within your body as key components of the immune system.
Image from www.physics.purdue.edu/people/faculty/nolte.shtml
"Fusion proteins" are proteins that are composed of more than one source proteins combined into a single polypeptide. They are highly related to "chimeric proteins"
By this, what we mean is that you may want to use standard assembly to encode proteins that are themselves composite parts of individual subunits. One of the most common applications of