According to Briess:
Carapils adds body, mouthfeel and improves head retention by adding dextrines, proteins, non-starch polysaccharides, and other body-building compounds into your wort.
I've used at up to 5%, body and mouthfeel yes, but didn't get too much head retention. YMMV, that's me with my process.
Never used Carafoam myself, but it supposed to be similar except to add a tiny bit of sweetness. IDK.
Am currently trying a few batches using Chit Malt instead to enhance the foam retention. First up in an Irish Red. Not sure why, but Chit Malt is only available from Best or Castle Malting. If there are advantages, then why have other maltsters not created an equivalent. Or have they? Anyway, the only way to know is to make a few batches and judge for myself.