[Spoiler warning for Bleach]
I've been watching a bit more anime of late and hearing about the annoyance, hatred and even fear that people have towards filler. Fear of filler seems absurd, but there are a people who have turned away from an interesting show because it was known for its large amount of filler.
As some probably would guess, the show I'm referring to is Bleach, which has a reported 46% of its episodes being filler (http://www.animefillerlist.com/shows/bleach) and whole arcs and movies have been deemed non-canon. While some of it absolutely is terrible, I personally don't believe that filler in general is a bad thing, at least under the current definition.
To make sure that I wasn't talking complete garbage, I checked up a definition of filler. For an anime, the generally accepted definition seems to be episodes that aren't based on their associated manga. This is pretty flimsy as there are quite a few animes out there that don't follow their original mangas perfectly, Hellsing for example, and others where the anime has actually gone on further than the manga, such as Overlord and No Game No Life. What happens in situations like Accel World where they refer to things that were anime exclusive?
Discussing this point serves for no real benefit however so instead we will consider another point that usually is included in the definition; An episode that does not further the story. This is the definition that I prefer for filler as an episode that does not further the story is one which can be skipped with no real impact. These episodes represent wastage or at least they should.
Consider episode 131 of One Piece, The First Patient! The Untold Story of the Rumble Ball! It doesn't contribute to the story - it can't because it falls between the Alabasta Arc and the Skypeia Arc. However, this doesn't make the story useless. Instead, it provides further exploration of a main character, in this case Chopper, which adds to the narrative. Considering the narrative and story separately to me, seems to be a mistake.
Instead, I propose a new definition for filler; the broadest of which is an episode that do not contribute to the narrative. You could argue that there's no way that an episode could be classed as filler, but that's certainly not true.
Take Bleach and the hated Bount arc. While it's traditional filler and non-canon, I wouldn't call the whole arc filler under the new definition. The events of the arc help flesh out the upcoming conflict between Ichigo and his hollow self , with one of the Bount's actually giving advice about denying that part of himself. The main invasion also helps with the narrative by building on reshi manipulation, which was only covered briefly when Urio broke his bow. These are sme of the reasons why I personally did get some enjoyment out of the Bounts.
While, in my opinion, the arc as a whole can't be considered filler, there are episodes within it that can. Consider the Bleach episode Assault from a Formidable Enemy! A Tiny Final Line of Defense?! They're supposed to be coming up with plans to fight the Bounts, but by the end of the episode the only new thing that's been introduced (a suit that amplifies the powers of Mod Souls) has been written off as something that they should never use due to their appearance.
All shows should strive for zero filler, but some times that isn't possible. This change would make zero filler episodes is a lot more achievable, actively aimed for as filler would literally be the content that serves only to waste the time of the cast, crew and consumer.