[narsil]

It's helpful to filter out links to large content and downloadable assets from being traversed. For example, I assume you wouldn't care about downloading videos, images, and other assets that would otherwise use a large amount of data transfer and increase costs.

If the file type isn't clear, the response headers would still include the Content-Length for non-chunked downloads, and the Content-Disposition header may contain the file name with extension for assets meant to be downloaded rather than displayed on a page. Response headers can be parsed prior to downloading the entire body.