Converting WebP to JPG gives you a plain photo file that older programs, print services and upload forms accept. For an ordinary picture nothing visible changes. JPG has no transparency and no animation, though, so a see-through WebP gains a solid background and an animated one is reduced to a single frame.
Transfers use HTTPS, and files converted on the free tier are deleted within 24 hours, so the result is not a long-term archive. Quality depends on the source file, so open the JPG file once before you share it.
FromWebPLossyTransparency
WebP (Web Picture format)
Google's image format for the web, released in 2010. One file type covers lossy photos, lossless graphics, alpha transparency and animation, usually at a smaller size than JPG or PNG. All current browsers display it, though desktop software support is uneven.
ToJPGLossy
JPEG (Joint Photographic Experts Group)
A photographic format that compresses by discarding detail the eye tends to miss. A JPG holds a single opaque frame, with no transparency and no animation, and is the safe default for cameras, printers, documents and upload forms.