Creating products one-by-one is fine if you're only selling a few products, but many people choose Magento as a platform to sell hundreds and thousands of different products. Entering each product individually can take a long time, especially if you're writing unique product descriptions, uploading photos, and adding crosslinked products.
With Version 2.0.1, Magento has greatly improved the performance of product imports. In previous versions, importing thousands of products could take hours – literally. We once tried to import 19,000 products and the job took 20 hours to complete! The improvements to Magento importing have greatly decreased that time.