Circuits... It's not just for making tetris.

[Miravlix]

It's a really important feature that the basic smelter keeps producing, but it's a lot less useful when things are automated, as you will end up with 100 * smelter iron/copper/steel plates that will never get used.

For a 48 row we get 4800 plates, so for a four lane bus that is 19200 iron plates, just sitting in machines and can only be accessed by manually picking them up and while I could use a few plates to handcraft stuff, 19200 is a bit much.

If you instead link input (enable/disable, anything = 0) and output (none, read hand, hold) inserters the smelter stops when output is blocked, resulting in at most 2-3 items in each smelter.

Some could make an argument for buffering *shudder*, but then 19200 plates isn't much and your better of with a nice circuit controlled chest buffer.

[shadetheartist]

So what if the plates aren't used right away? If a plate isn't being used its on a belt, if it isn't on a belt its in a furnace, if its not in a furnace its in the ground. You would rather have the iron in the ground than cached and usable.

Nothing wrong with that, its a preference thing. But there's nothing objectively better about it. And, really, the root of the issue is that your factories aren't ratio'd to consume what is being produced so instead of restricting caching just use the damn materials as they are produced.

[Koub]

There is no such thing as overproduction in Factorio. Either you lack ressources (get moar !), or you underproduce with the ressources (build moar !)
btw combinators are also terribly useful for making game of life within Factorio, or a player that replays Darude Sandstorm video in color.
Totally useless, thus totally essential