Even if you don’t spin your own yarn, I would argue that buying a wool winder should be the next purchase for the new yarn crafter, after yarn and needles or hooks. Why? Because of exploded skeins like the one below.

Can you wind your own balls of yarn without a wool winder? Yes, of course, but it takes more time and two hands. The wool winder gives me some extra holding power, so I can gentle tease the yarn from the snarled mess into a neater form without said form rolling off the table and onto the floor.

Having a wool winder also opens up more yarn buying opportunities. Many yarns in local yarn shops (LYS) or fiber shows have some beautiful yarn sold in hanks, large circles of yarn that must be wound off before use. Most yarn shops and fiber shows also have people manning a winding station and will wind off your yarn for free or a small charge. But what if you forget to stop at the station? There are choices, but an inexpensive wool winder is a worthy investment. Plus, it is satisfying to see the yarn build up on the winder.
After the winder, I recommend some kind of yarn swift, to hold the hank open. You can use a willing set of hands, or the back of a chair, but swifts are also a fulfilling basic machine to watch at work.