It is *much* more convenient. When a research path takes me to an article or book - I could buy or order or go to a physical library, that would take hours or days. I could also open it as a PDF in seconds. If you need to read a chapter from a book, or an article, or skim such checking to see if it's worthwhile, 20-30 times to figure something out, then libgen is the difference between finishing in a day or a month.