In reply to Mical:
They're very good in horizontal breaks — particularly shallow or flaring ones where a cam wouldn't work so well — and in oddities like shot holes. The pink in particular has a reputation for 'going anywhere', and I think the pink and red are probably the most useful two sizes if you don't have a particular use in mind. I used to carry them everywhere before I obtained a sensible set of cams, and a few months ago I added them back to my standard rack, racked with my big nuts.
You can place them passively like a normal (if oddly-shaped nut), but you can also place them in a camming sort of way. You ideally want the pointy bit behind a constriction, sling running between the rails from the back/top to the front/bottom of the placement so that it tries to pivot when pulled on. Give it a sharp tug to seat. Hard to explain but really easy to see if you have a little play. They're a bit fiddly to place unless you have two hands free though, and can sometimes be a nightmare to clean. Using a nut key to 'de-cam' it works, as can hooking a nut key behind the fulcrum. If your second isn't familiar, give them a quick briefing before they encounter them mid-pitch.