“Static” means it can be cached for a site (that is, the file is not dynamically generated). Examples include images and CSS generated from LESS. Magento uses static files to improve the system performance. You can find more details on the links below:
Thanks for your reply. Unfortunately these links don't work.
I think one reason seems to be that some of those files MIGHT be run over by a preprocessor. Ie. it is possible to minify and merge js files. I guess if for example preprocessors run over a template file the "final" version is then placed into the static files so next time the preprocessors won't have to run over it again.
So with sometimes it being just symlinks it just seems to be unnecessary.