I'm working on a project which generates images in multiples sizes, and also converts to WEBP and AVIF.
The difference in file size is significant. It might not matter to you, but it matters to a lot of people.
Here's an example (the filename is the width):
Also, using the <picture></picture>
element, if the users' browsers don't support (or block) AVIF/WEBP, the original format is used. No harm in using them.
(I know this is a meme post, but some people are taking it seriously)