why do Shimano chains have direction?

This was a passing requirement for some Shimano 10 speed chains. Discontinued when 11 speed was introduced

The chains are absolutely still directional (asymmetric, as Shimano says). The engraved plates must face out, or the shifting of the system will suffer. Not all of their chains are directional--just some of the 10/11 speed models.

Basically, the RH plates are shaped to better grab the chainrings, while the LH plates better interface with the cassette.

Huge functional difference versus, say, a generic KMC? No, not really...but why pay for Dura Ace and get performance several tiers lower with the wrong chain?

Shimano 11 speed chains DEFINITELY are directional.
Why, I have no idea. I use KMC now on my Shimano drivetrain, their direction doesn't matter.

Upside down or rightside up.. the engraving can face out, but the chain will have a different leading edge for each of these possibilities. I thought I read it's more important due to the shaping/material of the inside plates, and not the direction per se.

I thought *all* chains came with directions!

Srsly, thanks for the info from others ^^ about Shimano chains. I had no idea. Makes no difference to me, though, because I use Wippermann and SRAM chains because they don't have those silly replacement pins.
Steve

Shimano finally now uses a quickie link like KMC and SRAM. No more drive in, snap off pins.

Link plate shapes are different? did you look?

Heh. I use SRAM 11s chains because they're cheaper at the lbs than 11s Shimano or kmc chains on Amazon.

Because the inner side is shaped for better shifting on the cassette and the outer side is for better shifting on the chain rings. Non directional chains like KMC still works, just fine.