Correct, EJ. The main culprit for which grease bands are used is the Winter Moth - the females of which cannot fly and are therefore condemned to crawling - but, of course, there are various other less devastating insects which are caught. The Winter Moth should not be confused with the Codling Moth, the caterpillars of which climb the trees in June and July. These are best prevented by using strips of sacking or haybands around the trunks about a foot or so above ground level during those two months, after which they should be removed and burnt.
I should also have added to my previous answer that the hessian or cloth bands should be at least 10 inches wide to be effective, and, of course, it is necessary to renew the grease (or vaseline) periodically throughout the winter until the bands are removed in May. Please also remember that if the tree is staked it is necessary to treat the stake as well to prevent the moths bypassing the bands.