A little of both. I put the browser, os and device type info into my data layer. I use that to decorate some of our API performance logging. I also use it in a couple of DTM rules. It is a handy way to get some basic info without having to parse the userAgent string myself. It won't be killer if it is not available in Launch, but it sure is convenient.
And speaking of the new cookie() function - where is the documentation on that? I looked, but no luck.