As Simon indicates 'it floats'. Bearing that in mind an oily additive can be advantageous as to indicating when you have 'active' fish in the swim as small globules of oil will rise to the surface as the bait/s are disturbed.
Stick a flavour of your choice in it and you have a home made glug. Sesame oil (with or without garlic) has a good reputation and is something I mean to try sometime. Let's hope the fish like it as much as I do.