I have the same question. In Taylor's book, he does this in his example of getting rid of the Models folder:

"autoload": { "psr-0": { "QuickBill": "app/" } }

Excerpt From: Taylor Otwell. “Laravel: From Apprentice To Artisan.” iBooks.

With PSR-0/PSR-4, you don't have to dump-autoload when you add or update a class. With @dwenaus's example, you could put helper.php at app/helper.php with namespace QuickBill, or maybe app/helpers/helper.php with namespace QuickBill\Helpers, and you wouldn't have to dump-autoload changes to helper.php.

I only use classmap for non-namespaced classes which don't fit my normal PSR-4 rules. Specifically, app/database/migrations (see this comment), app/database/seeds/DatabaseSeeder.php and app/test/TestCase.php.