One of the things I like about Honor Harrington is how people move in and out of the books. Some of her crew from the very first novel disappeared for a few books afterwards and then reappaer in a new position. Its fun to see them advance through their careers along with Honor even if they aren't th focus of the book.
To be honest though, sometimes a character will disappear for 3 or 4 books and when they come back it takes me a while to remember who they were, haha.
The Wheel of Time is a good example of a central cast of characters we get to know but then there are sooo many throw away characters it can get confusing. Usually if an author spends several pages telling me about a character's looks/family/history/thoughts, they have some role to play. In the Wheel of Time, these characters are sometimes used just to show a changing world and then are never mentioned again or seen once in passing a few books later.