JPG: great for photographs
If an image contains lots of color gradients, such as a camera photo or a landscape, JPG is often practical. It uses lossy compression, but that trade-off can produce a small file that is easy to share and serve on the web.
PNG: when sharp details and transparency matter
Logos, simple graphics, and some screenshots can benefit from PNG, especially when sharp edges or transparency matter. The downside is that PNG can become very large for big photographic images, where another format may be more efficient.
WebP: a strong web option
WebP is a strong web-oriented option because it can provide good compression while keeping useful visual quality. Before making it the default in an older workflow, make sure the system receiving the files supports it.
Do not judge by the extension alone
A 400 KB JPG can be a better choice than a 3 MB PNG for one job, while the opposite can be true for a simple graphic. Compare both visible quality and file size. The goal is not to pick the most fashionable extension; it is to pick the format that fits the content.
A rule worth remembering
Photograph? Start with JPG or WebP. Logo or graphic that needs transparency? Consider PNG or WebP with transparency. Image for a website? Test WebP when your stack supports it. Then judge the actual result rather than the format name alone.
Remember metadata and color information
Changing format can remove some metadata, and colors may look slightly different between applications when an image depends on a specific color profile. That is rarely a problem for everyday sharing, but print work or photos that need EXIF data deserve a test conversion before processing a whole library.