Questions About reSmush.it Size and Quality Standards

Hello,

Before downloading this plug in, I have some questions. Can you please help me understand..

– What is a good standard for “smushing images”? Does smush have a target kb or reduction % it aims for?
– How does this tool know how low to smush without losing quality?
– Can sizes be set for images that will be used differently on the site, like a product photo versus a banner photo?
– Will we need to continue to compress/optimize images in advance of uploading them and smushing them? Do we need to worry about an image being over smushed?
– Are there file types that this will not compress?
+ Will it create duplicate images in the media gallery? (The uploaded and the compressed versions)

Curious,
Jennifer