Most of my money comes from NIH. Beyond scientific justifications, there are some practical ones, but I’ll save that for later. I have a small (by definition) grant from NSF, and have sat on NSF panels from time to time.
The most recent panel was one of the directorates that moved to once a year submissions. That’s not as bad as it sounds, because about half the proposals go through two steps of review, and two sets of comments in that year.
One of the things that hit me, which is really different from NIH, is the role of “Broader Impacts” which is only vaguely related to “Significance” in an NIH grant. In the Olden Days, it used to be OK to say you would recruit women and URM undergrads and grads to your project. These days, women don’t count (imagine that) as they are more than 50% of these populations. Furthermore, everyone says they will recruit URM’s now.
So you have to do something different to stand out, and make your response in this category count. I read lots of things about outreach to disadvantaged schools, inner city museums, etc. One of the things that seemed to matter was having done this before. That is, saying something you have been doing all along, not just not something you will pick up when you get funded,
There was also an interesting discussion about whether blogging counted as a greater impact. The blogging people who got good scores on this were ones who had blogged for a while and who could demonstrate significant traffic (by statistics). The PZ Myers of this world (whatever you think about his politics and his feminist credentials) do well, and the guy who is just starting a blog about the sadness of endangered species does not.
As always, talking to someone who has been there and watched the process is usually helpful, and helpful not the week before the grant goes in, but when you first start planning it.