Truth is that the yarns and spinning fibers at this level of the market have already been washed a couple of times. They may not have been scoured, but all that is needed to remove residual lanolin and spinning oils is a couple of hot baths. I plunge my yarn into a warm bath and let it soak for about 20 minutes, then gently squeeze water from the skein and repeat until the water is no longer milky looking.
The same treatment is used for roving, but more care has to be taken when lifting heavy wet roving from a bath so that it does not tear or mat together. Just put your hands under the roving, down in the bath, and sort of gather it together while it is still in the water. You may even want to drop it into a colander and give a few gentle pushes from the top to get out the water.
If you're using raw fleece or yarns spun from raw roving, yes, they'd need to be scoured, but these yarns are commercially prepared and are a far cry from raw fleece with the dirt, straw and unmentionables found in the fibers. These yarns and spinning fibers do not need to be boiled and stirred at all, just washed or rinsed in a couple of hot baths.
The less rough handling of the fiber, the better your result. Avoid heavy stirring in the pot, or if you cannot contain yourself, be sure to add several extra choke-ties to the skein before you wet it. Same thing goes for roving and spinning fibers: use a gentle hand. If you're doing an open pot method of dyeing, then get a big spatula to lift the fiber in the pot and distribute the color, always taking care not to allow the fiber to support the weight of the rest of the material and the water, which, of course, will pull it apart. Even when dyeing roving, there's no need to smush and push and agitate the color into the fiber at all! Just apply it, gently blot the color into the fiber and let nature/osmosis/color bleeding/heat take its course.
Felted yarn is hard to get into a usable state. It's time to pull out the imaginative ideas to work with felted yarn, and I will leave that concept alone for now. Felted fiber can be saved by working with it to fluff it up, stretching gently in all directions along the length of the roving. Another method is the thigh-thwacking procedure! Yes, a technical term which aptly describes a way to introduce air between the little matted fibers while offering some exercise to the fiber enthusiast at the same time.