I'm not totally convinced that cronin2 is going to feel 100% enlightened regards their question, so at risk of further confusing the issue (and of further talking playlists in the Portable Devices board), here's my take on the question asked:
Filters apply only to the
Music node and reside in that node as a subset of 'Music':

Filters are relatively basic methods of restricting what is displayed by the use of one or more rules. They are ideally suited to splitting your library into subsets in order to make browsing easier and/or setting different views for different sections of your library. The example above shows two filters - one for Classical music and one for everything else, This allows for the Classical music section to be set to display Composer, Conductor as opposed to, or in addition to, Album Artist etc. Maybe you have a collection of stand-up comedy or poetry or political rants you would like to browse separately.
Navigation between them is easily done by selecting the required filter in the Navigator panel (as shown), or by assigning each to its own tab.
Auto-playlists are similar in that they are configured by a set of rules but these are much more powerful tools having several additional configuration options. They reside in the Playlists node and can use any node (or filter) as a source - as has been discussed above. Generally used to make selections of tracks to play as an auto-updating playlist (as opposed to a static playlist), their uses are myriad, pretty much limited only by your imagination. As I have a very limited imagination, here are all of my thoughts:
- Genre playlist: 1 hour of 'Ska-Jazz' selected by most recently added tracks.
- Mood playlist: 20 'sad' tracks selected at random.
- Best Of playlist: 10 tracks by Artist X selected by highest rated.
- Cover version playlist: 25 tracks, tagged as 'covers', rated> 3 star, selected at random.
- Collate several playlists into a single one: Playlist is any of Playlist1, Playlist2, Playlist3.
Can also be used as tools when tidying, re-tagging or sorting your library (but I guess filters could also do these):
- Find specific filetypes: Ext is .mp3.
- Find tracks with no lyrics: Lyrics? has no value.
- Find low quality tracks: Bitrate is less than 256.
+ + + + +
Of course the more attention you pay to tagging your collection, the more powerful auto-playlists become.
I hope this may have been of some help. Note that this is only an idea of what these can be used for, and others may have differing opinions.
(And then there are
Playlist Mixers but that is a story for another time - this has already become much longer than anticipated.)