So you are sitting at your wheel and you have a hank of fiber in front of you. Do you just start spinning? Let me ask you to wait and think about a few things first.
What is your goal for this fiber? Are you looking for warm hat, hard wearing socks or are you just spinning to spin?
Spinning just to spin is fine. It gives you a chance to play with techniques and relieve the stress of everyday life.
But if you have a project in mind then your choice of spinning will affect your results.
Let’s first talk about what woolen and worsted spinning is. Think about them like they are two end points on a line.
With woolen spinning your preparation needs to be either random order or semi random like a rolag and your drafting zone is longer than the length of the fiber. This produces a ply with more bounce and a structure that helps trap air.
Worsted spinning uses combed top that is very ordered and uniform length for the individual fibers. The drafting zone is less than the length of the fibers. This produces a smooth, compact yarn that incorporates little air in its structure.
Now those are two extremes. Between these is what people call semi-woolen and semi-worsted. Most fiber preps are not truly uniform or random. Cotton spinning is a great example. Cotton is spun woolen but the fiber prep is usually a sliver which is closer to worsted than woolen prep.
I would not fuss too much about if you are spinning just to spin and relax. However if you are spinning for a project you need to pay greater attention.
Some examples of projects that are better suited to worsted spun yarn include socks, woven suiting and lace. Woolen spun for hats, some scarves, and woven blankets that are fulled.
Of course there are exceptions to the rules such as my woolen spun Shetland/Shetland blend shawl and warm bed socks made of alpaca.
Once again, these are not hard and fast rules, and when you are outside the sphere of europeon influence these constructs are not discussed as such. But I find them a useful guide to making the right yarn for the right project.