The different tiers of crafting skills represent the different levels that you can personally craft.
Our crafting, like in many games, will be broken into these tiers - 1, 2, 3 - that represent how powerful the item is, how useful it is, and how many resources it requires.
While we haven't fully worked out the crafting skills, here are some examples with Device Construction. These may or may not be items since I'm not handling crafting, but I believe they are appropriate levels of power.
You may get a tier one schematic that allows you to contruct a device that gives you a cheap kit to cut down the time on the repair skill from 1 minute to 30 seconds for two uses, and two components.
A tier two device may allow you to throw a specialized spike that unravels once it pierces the bone, giving you a packet for "Maim by Device" for three components.
A tier three device may allow the wearer to Reduce a called weapon strike and Destroy the weapon that hit them for four components.
*Edit* ....or if that's too long, what Ian said above me