There are more than 200 species of potatoes, but they all contain two primary components, starch and moisture. Low starch potatoes give a firm, waxy texture and maintain shape after boiling. High starch potatoes give a crumbly, mealy texture, and become soft after boiling.
Low starch potatoes include small round red or white potatoes with a thin skin, such as Red Bliss potatoes. They are good for boiling, stewing, or chunkier mashed potatoes. Low starch potatoes absorb less liquid, thus yielding a firmer texture.
High starch potatoes include oblong Russets with thick skins. They are easy to mash and make great baked potatoes. High starch potatoes absorb more liquid, which easily breaks for a fluffy texture.
Yukon Gold potatoes fall in between these two and can be used either way.
Source: The Science of Good Cooking, Cook’s Illustrated