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Drop one GIF or two hundred. Batch conversion is not a paid feature here.
A single frame from a GIF needs to become a normal photo file for a document, a listing or an upload form that rejects GIF.
The GIF's indexed palette is expanded to full RGB and then JPEG-compressed. For a photographic GIF the file usually shrinks; for a flat-colour graphic it can easily grow.
The two formats fail in opposite directions. GIF already banded the image into 256 colours, and JPEG now adds ringing around every one of those hard band edges. Flat graphics look visibly worse. Use PNG for those instead.
The first. A JPEG holds one image, so an animation has to be reduced to a single frame.
No. JPEG has no alpha channel, so transparent pixels are filled, normally with white.
Drop one GIF or two hundred. Batch conversion is not a paid feature here.
JPEG Image is lossy, so the quality control decides the trade between size and fidelity.
Instant, because the file never went anywhere. Nothing expires, since nothing was stored.