Not necessary, but a nice accessory to have
The easiest way to manage a solar pool cover is to buy a reel that allows you to roll it up when you want to swim and unroll it when you want to cover the pool again. Reels are VERY nice! But they don’t work well on some pools. My pool, for instance, has a jumping rock at one end and the pool entrance at the other end, so there’s no place to put the reel. It’s also very narrow at the entrance and wide at the foot. So even if we had a mobile reel and wanted to pull it into position to uncover the pool and then move it while we swam, the shape of the pool makes it fairly unmanageable.
If you can’t afford a reel or don’t have room for one, it’s easy enough to just pull your solar cover off and fold it near the edge of the pool while you swim. But if you can afford it, a reel is REAL nice.