Compression level controls how aggressively the tool reduces color detail and optimizes the GIF palette. Low compression keeps more visual detail and is best for brand assets, UI recordings, product demos, or GIFs with small text. Medium compression is the best default because it usually cuts file size while keeping edges, captions, and motion acceptable. High compression is for strict targets such as Discord limits, email attachments, or compressing GIF to under 1MB.
A practical rule is to start with medium compression, then move to high only if the output is still too large. If high compression creates noisy gradients or rough text, switch back to medium and reduce width or FPS instead. For simple reaction GIFs, high compression is often fine. For tutorials and screenshots, medium compression plus resizing usually looks cleaner.