I'm not really into "canon" - I don't need my fiction to be knowable in advance to other RPGers. When I've wanted to explain it to them, I've generally found myself able to do so.
My relationship with "official" is more complicated. I have no problem with introducing new game material where it is warranted - on the weekend I ran a session of Agon using
the island I wrote up for "Not the Iron DM"; in my 4e D&D campaign I used plenty of game elements (eg creatures) that I made up myself; as a Rolemaster GM I authored my own systems for initiative, PC building, etc (which is practically compulsory for a serious RM GM).
But I do find quite a bit of "homebrewed" material that I encounter is not very well designed. In the context of D&D, this mostly consists in it being mathematically out-of-whack with the core game system. Or otherwise not showing a great degree of awareness of the "aesthetics" of the system. Outside of D&D, one encounters much less material "homebrewed" or otherwise, but there can also be issues there: eg in the Prince Valiant episode book there are plenty of NPCs who do not conform to the character building rules but with no obvious reason for this, and which therefore sit in tension with Greg Stafford's own advice in the core rulebook and his painstaking reconstruction of such characters as Arthur, Guinevere, Lancelot and others in accordance with those rules.
There can also be material that is designed without much thought to its effect on the dynamics or experience of play. Vincent Baker tackles this directly in his advice on custom moves in Apocalypse World, and
John Harper has also written about it. This particular sort of poor design can also be found in "official" material eg a lot of the 4e adventures published by WotC.
I guess the upshot is that, for me, "official" is not about having a common language; but screening material with a slightly sceptical eye is about the particular qualities of the gaming experience.