Pick the strength that matches the image
Low keeps more detail and usually saves less space. Maximum pushes the file smaller and can look soft on text or fine edges. Balanced is a sensible start for photos.
If the new file is not smaller, the tool keeps the original bytes and says so. You can then try a stronger level, resize the image, or switch to WebP.
When a fixed size is the real limit
Some forms and chat apps care about kilobytes, not a quality slider. Use a target-size page when you need the file at or below 100 KB, 200 KB, 500 KB, or 1 MB.