Is it just me or does this not actually do what the docs say about it. According to the PHP documentation:
The MAX_FILE_SIZE hidden field (measured in bytes) must precede the file input field, and its value is the maximum filesize accepted by PHP. This form element should always be used as it saves users the trouble of waiting for a big file being transferred only to find that it was too large and the transfer failed.
To me, that sounds like the file upload is supposed to cut off immediately once the number of bytes transferred exceeds whatever value is in this MAX_FILE_SIZE hidden field. I've tested this (by using Chrome Dev Tools to simulate a slow connection) and the request still seems to wait for the entire request to complete. The parameter does get used though, and I end up with a FILES array element error containing a UPLOAD_ERR_FORM_SIZE value but is the documentation just wrong, or am I reading it wrong?