Plying is necessary to strengthen the wool you have spun. If you can spin you can ply. I found it easier to learn than spinning and plied the first wool I had ever spun. I need more practice because my plying is a bit loose. I don't mind because anything I am making is a big step forward and anything I learn can be improved. I can spin thinner yarn now and can do that consistently which I couldn't before. Washing in cold water first with some wool wash or pure soap is a good idea and then you can run it through warm water. Not hot. You then get as much water out of it as you can before you dry it. Going to be a bit of a challenge in the cold weather! Plying means you can ply your handspun wool with any other wool. You can create different weights and textures so if you are looking to make original wool then plying is a good skill to have. You don't have to have to ply your own spun wool. It gives you options and choices.