I found time not so trivial when reading several files with 300 M + lines. It also makes the loop cleaner by removing from it things that don't need to be in it. It also make the algorithm slightly simpler when reading a sorted file to remove duplicates or reading in parallel two (or more) files sorted according to the same key to compare data.

As for the my $useless_line = <$info>;, I would probably not really code it that way, but I thought giving such a name would make it more self-explanatory to the OP, you seem to disagree, maybe I was wrong, I don't know.