The truly experienced programmer doesn't conflate efficiency with effectiveness, but that's worth a separate discussion.

Using a regex to parse fixed-width fields does indeed sound like overkill, but using substr isn't necessarily the most effective alternative. Splitting a record with multiple fixed-width fields requires multiple calls to substr, along with cascading math to make sure that the substr's start at the right places. Contrast that with a regexp-based solution, which requires a single invocation of a regexp, and no additional bookeeping. And then there's the oft-overlooked unpack.

The psgrep example in The Perl Cookbook demonstrates a method for separating fixed-width fields by constructing a format string for unpack. It also demonstrates an elegant way of documenting how the format string is assembled.