Loosing the last boats - very important. We race mostly on weeknights and the last boats can get stuck as the sun goes down taking the wind with it.
We race one-design, of course, and we have a weeknight series and a Sunday series.
With one-design, you keep from losing the last-place boat by having very short races (ours are 20 minutes long), so the last place boat is still finishing within a couple minutes of the first-place boat. And because we are able to get more races in, everybody keeps getting another chance to learn from their mistakes and try to correct them for the next one.
The after-races-group-debriefing-and-beer session gives everybody a chance to figure out what they did right or wrong and why.
In our case, the only boats that get stuck in the doldrums when the wind goes down at sunset are the boats that pick up the marks after the races.