JPG turns the visible canvas into one opaque image
A PSD can contain layers, masks, text, and transparent canvas areas. JPG combines the visible appearance into a flat picture and cannot store transparency. Decide what background should show before export; an empty canvas is not the same as a white background in the final image.
Once flattened, objects cannot be moved independently in the JPG. Keep the PSD if another designer may need to edit wording, positioning, or effects. Use the JPG for a preview, email attachment, or service that accepts only a common photographic image format.