The advantage is that the regex you are running over the sliding binary chunks will be smaller, and (I think) therefore faster. So I figured it would be more efficient on big files. If it's a really big file, most chunks won't match, so why test a regex string of length 1000, when a test on length 250 will give a quick "sniff", indicating whether you should dig deeper at that general area.

But as always, I defer to your greater experience and wisdom. :-)