Why is 'X-Requested-With' request header added by default?

[dmnrmr]

There is also no way to remove it from request headers.

[whiteinge]

It's a pretty strong convention going back over a decade: https://en.wikipedia.org/wiki/List_of_HTTP_header_fields#Common_non-standard_request_fields

Though it's probably not too useful nowadays. In any case, it's safe to ignore.