Playlists can be of use for grouping together movies by various search terms. For example, all Star Wars movies or all films by a certain director. It saves time of having to setup the search criteria manually in the future. Playlists can be setup manually by the user but will not reflect new additional to the library automatically. This is why I recommend using a specific search criteria to automatically handle the addition of new library items.
If I wanted to create a playlist for only Star Wars I would navigate to the Movies library and click on the left most filter and choose Custom Filter. Since Plex has collections for movies that are in a series I can choose the Star Wars collection as shown below. Click Apply and Plex will display matches to the selected filter.
Now that the filter is applied we can create the playlist by clicking the Add to Playlist button and entering a name. Save the playlist and click on the Playlist library.
The example above shows on the left a manual playlist and on the right is an automatic updating playlist. The gear icon in the top left indicates the playlist will auto update. In this example, when a new Star Wars movie is added when the playlist is opened it will reflect the new movie.
