Candying ginger is one way to preserve what remains of the root after the required amount has been used for a recipe. If it just sits around, by the time it's needed again it will have shriveled and/or molded. On the other hand, if there is evidence of eyes that might sprout, it might be better to encourage them to do so and try to plant and grow some ginger. That's often successful and returns bountiful harvests.
This recipe was found on the Daring Gourmet site. It calls for a hefty amount of ginger, 1 lb! That's more than is ever brought home, let alone remains after a recipe. Usually working with something more like 100 g. So the quantities are scaled down. More like 1/4 C of reserved water from the boiling and 1 C of sugar for the final cook.
Peeling is done with the edge of a spoon. That works great. Gets into the curves of the root nicely and just rubs off the skin without losing any of the underlying core. Occasionally the insides have a blue tinge. That reflects the age and/or way the root was stored. Not harmful. Recipe recommends using a mandolin to do the slicing. Hasn't worked here. Use a good sharp knife. Works fine.
Final drying is done in the dehydrator to speed things up. The syrup is always preserved. It has a wonderful ginger flavor that goes well in so many sweet dishes. Almost worth doing this just for the syrup, alone.