Definitely not a time-saving measure. The time limiting factor is the actual getting-on-the-plane-and-putting-your-carryon-away-and-getting-out-of-the-aisle part. Often I get my boarding pass scanned and go stand in line on the gangway.

In fact a mathematical algorithm was developed for loading faster[1] but I'm not sure anybody tried that yet.

[1] https://phys.org/news/2008-02-board-plane.html