Inventory is the cardinal sin of the Lean philosophy, as it brings with it all its other ugly buddies (transport, movement, waiting, overproduction, overprocessing, defects and underutilizing skills).
In the material world, mentioning "Inventory" will generate an image of an enormous warehouse, painstakingly maintained, expensively rented... In the case of incontinent composers like me, it is more like an enormous computer folder, full of subfolders with .wavs, .oggs, .mp3s, .docs and what have you... Plus this other "warehouse", harder to pinpoint because it only shows intermittently, that lives in your brain and in your guts.
It is this second inventory that is the hardest to manage. What makes it particularly so is the fact that it is alive; the moment any of those proto-songs receive any "air time" from my brain, they change, they mutate. It's like a collection of uncaged animals, feeding on what they have around (sometimes other animals), and evolving in unexpected shapes. And they don't stay still.
So I sometimes run into this peculiar situation: I'm filling the gaps of a song I want to take to production, it consolidates, it pumps, I'm happy of how everything is coming along, and then, in one of my sessions, I realize: this or that part is a plagiarism. A plagiarism of another of my songs, ANOTHER SONG THAT I HAVEN'T EVEN RELEASED YET.
So nobody would ever notice. Heck, perhaps, even when both songs were released, nobody would ever know or care either. But here, with me being the author, someone with skin in the game, there's a different matter at stake: self preservation.
What happens next is often disagreeable and frustrating (especially when it's taken me long to discover the self-plagiarism an the song was already very mature in my view), but whenever I run into one of these issues, I stop and take the time to dismantle and change the song. Sometimes it takes forever (and time after time, ah the frustration, the new stuff I try ends up turning out to be a covert variation of what I already had; I guess there was a neural path already created and you tend to glide through it again). But the way I see it, not doing so, skipping the fact, is a dangerous form of laziness, bad maintenance of your own creativity. If the song that I'm making does not surprise myself, why bother? Playing it would become "homework" for me. I prefer to take my time, although sometimes the process bores me like hell, feels unnatural, etc...
Sometimes all that was needed was a variation in some sense; we all know records or books that have "siamese" songs or stories, and we love both. All is good as long as such similarity is intentional, some kind of lateral exploration the author considered worthwhile to pursuit. The problem is when the only intention behind is "let's get this over with". There are musicians, there are albums that are like that, and it's not beautiful.
And again from the point of view of the inner realm, I think letting go like that is a dangerous path to follow. Just like body articulations become stiffer with years and you have to be vigilant of it and maybe take additional measures, there is a counterpart in the mental realm. For the mature artist, as the heap of his production grows, it becomes easier and easier to just go for what you know, just chop pieces of things you've already done and assemble them in a different order, like Lego bricks.
I'm not saying that this kind of creations completely lack value sometimes; as a listener, I can still play and enjoy some of those albums (particularly, if the original pieces had great quality, there are always interesting and moving things to find in the derivative works). But as a creator, I don't want to follow that road. I prefer to become a slower composer, taking as long as it takes till the song is done, but when it finally is, being sure that it is "its own little ride" in some way. Life has too much homework already.
Probably, if the animals didn't spend so much time captive in the warehouse (years sometimes), they wouldn't get so impatient, and wouldn't have so much time to bite and hump each other... And that, kids, is another reason why inventory is bad, and it's imperative that I increase my productive capability :)
I have a guitar and I'm gonna use it