There's a "hidden" optimization, where setting this option to -1 actually avoids the User-Agent: parsing etc. entirely. I'm suggesting we make this be the default, and later examine if we even need this feature at all. (The intention with this feature is to do UA sniffing, and inject some headers depending on the string matching MSIE or not). This was a problem ~10 years ago, unclear if it's still necessary at all.