[Spinnthrift]

Let's look at Sheep Leather as a x1 synth:

1x Dark Crystal + 1x Windurstian Tea Leaves + 1x Distilled Water + 1x Sheep Skin. = 1x Sheep Leather.

Now, when you go farming leather in the field (so to speak), you need to take ingredients to synth with... so, for each stack of leather, you need to bring 12x Dark Crystals, 12x Tea Leaves and 12x Distilled Water.. taking up 3 inventory spaces.

With Tanning, the synth changes to:

1x Dark Crystal + 3 Windurstian Tea Leaves + 1x Distilled Water + 1x Tanning Vat + 3 Sheepskin = 3x Sheep Leather.

So to make a stack of Sheep Leather, I need to bring:
4 Dark Crystals, 12x Tea Leaves, 4x Distilled Water and 4x Tanning Vats. This takes up four slots in inventory, compared to three with the previous recipe... however...

To make two stacks of Sheep leather.. you need either:

24x D.Crystals, 24x W.T.Leaves's, 24x D. Water and 24 S.Skins taking up 8 slots of inventory...

or..

8x D. Crystals, 24x W.T. Leaves, 8x D. Water, 8x T. Vats and 24 S.Skins taking up 7 slots of space...

Three stacks is 12 inv spaces with the original method, or 8 with tanning... and so on...

If that makes sense?