I once watched a client complain their homepage took forever to load. The culprit was 14 JPG photos, each straight off a camera, each around 4 MB. Nobody had touched them.
Converting those same photos to WebP would have cut the total weight by roughly two thirds. That's the whole argument for this conversion, in one sentence.
What WebP actually does differently
WebP squeezes the same photo into a smaller file. It uses smarter compression (the kind that throws away detail your eyes skip anyway). Google's own tests put the savings at around 25 to 35 percent versus JPG at similar quality. In my experience with real photos, it's often more.
The visual difference is basically nothing. Open a JPG and its WebP twin side by side and you won't spot which is which. The bytes disappear, the picture stays.
Where this conversion matters most
Websites. Specifically, any page where you control the images: blogs, portfolios, product pages, landing pages.
Page speed is one of the things search engines actually measure now. A faster site keeps visitors longer and ranks better. Converting your hero images and thumbnails to WebP is one of the easiest wins there is.
Where you should skip it
Don't convert photos you're sending to other people or archiving for years. JPG is readable by every program on earth. WebP is close, but "close" isn't the same when you're handing files to a client who opens them on a ten-year-old laptop.
And don't convert images that need transparency. WebP supports it, actually, but if transparency matters to you, PNG is the boring reliable answer.
Practical tip: convert and keep both files for a week. Drop the WebP versions on your site, keep the JPGs in a folder. If anything looks off, you have the originals. I've never needed to roll back, but the folder costs nothing.
Doing the conversion
Upload your JPGs to Jiggle X Wiggle's free converter, pick WebP, and download the results. Free, no account, nothing installed.
Then check your page load time before and after. That gap is why this format exists.