JPEG is designed to compress images efficiently, not to act as an endlessly editable master format. Repeatedly decoding, editing and saving a JPEG can introduce new compression loss each time.
What generation loss means
When an image is saved as JPEG, the encoder approximates visual information to reduce size. If that output is later decoded and compressed again, the second encoder works from an already approximated image. New artifacts can accumulate.
When the effect is noticeable
High-quality settings and light edits may make the change hard to see, while repeated low-quality saves can quickly damage fine texture, text and edges. Cropping or editing tools may also trigger a full re-encode depending on the software.
A safer workflow
Keep an original or high-quality master in a format suitable for editing, then generate JPEG, WebP or AVIF delivery copies as needed. If all you have is a JPEG, avoid unnecessary save cycles and export only when you actually need a new version.