Minifying CSS code contributes to fast downloading and parsing, which is considered economical. Besides, your code would be well protected, thanks to this tool.
The purpose of minifcation is to increase the speed of a website. Minimisation can make a script up to 20% smaller, resulting in a faster download time. Some developers will also use it to 'obfuscate' their code. This makes it difficult for the code to be read, thereby making it more difficult to reverse engineer or copy.
It is also common practice to combine all the CSS files for a single website into one file. This has a number of benefits. It reduces the number of HTTP r equest that need to be made to get all the elements of a website. It also makes minification and gzip compression more effective.
More information about Minification (Wikipedia)