With the default version of sails on npm (v.9?) --linker works ok i.e. creates /linker folder. I can copy js, css files to assets/linker/ and they appear in
Sails v0.10 no longer uses the linker folder--it was just causing confusion. If you have the linker option enabled, then any assets under your assets folder will be copied over to your .tmp/public folder by Grunt when Sails is lifted. The public folder will be created by Grunt as necessary. The grunt-sync task will then keep the folders synced as long as the program is running.
Sails projects are not dependent on Grunt, so renaming the Gruntfile (or removing it completely) won't stop the program from working, but that doesn't mean it's not doing anything when it's there! To see what Grunt is up to, you can lift Sails with sails lift --verbose.