See the current Perl documentation for lib:less.

Here is our local, out-dated (pre-5.6) version:

less - perl pragma to request less of something from the compiler

    use less;  # unimplemented

Currently unimplemented, this may someday be a compiler directive to make certain trade-offs, such as perhaps

    use less 'memory';
    use less 'CPU';
    use less 'fat';