Incorrect, sprite sheets are a HTTP/1.1 optimization. This is also a fragile and complex techinque that breaks, say, simply linking to a given emoji. HTTP 2, which we already use and have for quite a few months, doesn’t require these contortions.
https://mattwilcox.net/web-development/http2-for-front-end-web-developers
Now the advice “only load what is (currently) visible” is timeless, and damn I wish web browsers had implemented this back in 2002. (Try loading a long web page with 50 images, when 49 of them are not visible due to scroll position.)