I believe any yarn/thread can be used to knit/crochet anything, and there are no hard-set rules whatsoever. So, if a lace weight yarn is referred to as crochet thread, I could make lacy knitted shawls out of it too!
If you want to make tops/wearables, accessories like hairbands etc or home decor like cushion covers, bedspreads, etc for summers/hot weather then cotton is the best choice as this will keep you cool.
But if you want to make for winters/cooler climates then you can go for acrylic, acrylic/wool blends, pure wool, as these will keep you warm.
For blankets you can choose any yarn right from cotton to acrylic to polyester to wool. But you will need to choose depending upon your requirement – cool, warm or warmest, light or heavy, and size – baby to double bed.
For rugs, bathmats, carpets, try and use thick cotton yarns. These days you can even use macrame ropes as they are suitable for rugged use. You may not want to use a fine cotton yarn meant for wearable to land under your feet!
For Magic, in general, is an illusion. But for making tangible magic, you do need yarn, needles and hooks!
I have recommended the projects for all the varieties I have on my website. Though I may not have recommended a wool blend yarn for a rug/carpet, I have made it for a customer. So do feel free to explore, break the rules. I have prepared a project wise yarn recommendations below for easy reference..
Related Useful Links
◼ Yarn Recommendations by Project◼ Estimating How Much Yarn To Buy
◼ Yarn, Yarn Weight & Related Needle / Hook Sizes
