gzipping is a technique used by a webserver to pack static assets, helping to reduce the size of transmitted data by half or more. The gzip report just lets you know how much the technique will save, but it is obviously unable to compress the file beyond normal minification. This post has some further information if you're interested:
http://betterexplained.com/articles/how-to-optimize-your-site-with-gzip-compression/
Personally I'd turn gzip reporting off since it doesn't perform well; perhaps only save it for when you're ready to deploy.