When you click a movie, you want to see who's in it. But when you're browsing the top-level list of actors, you'd rather see the stars than every single actor in the world. The Filters preferences pane lets you choose to only show actors with a certain number of loaded movies. For example, if you choose to show people with at least five movies, then anyone in just one or two movies will be filtered out, making the list more manageable. You can also choose View ▶ Sort People ▶ by Number of Movies to make the biggest stars float to the top.
Similarly, you can filter genres, keywords, languages, and years by the number of movies. For example, it's cool to see all the movies that came out in 1994, but it's less interesting to have 1937 in the list because you have one classic movie from that year. If you choose to only show years with at least five movies, then you'll get a reasonable timeline. You can sort years in increasing or decreasing order.
Favorites are always included in lists.
You can also choose which movies to show under the top-level Recommendations header, but in this case it's the number of recommending movies that counts.