The science board, committee, council or whatever it is called is an important part of every grant application process. Often, they make the funding decision independent of the funding body. The receive important input from the expert reviewer(s) but they make the final call.

It is important to understand the working mechanisms and factors influencing their decision. Knowing the nuts and bolts of the process can help you to write a better proposal.

Unfortunately, it seems like a black box to most applicants. I did some google research and found a few publications and an interesting little video providing a little bit more insight.

 A 15 min video of a mock National Institutes of Health grant panel (USA) is a good watch for your lunch break.