Let's say: Mike doesn't want to use namespaces but he wants to use a
package from Jessie. Jessie uses namespaces. Mike has his PHP configured
to "auto-prefix-import" everything. So if he uses your file foo.php containg
namespace JessieStuff{ class Foo { ... } }
in conjunction with this setting would enable him to
require_once('foo.php');
$x=new JessieStuff_Foo();
So, if namespace JessieStuff contains multiple classes. They would all become JessieStuff_ClassName.
Assuming the package relies on its own classes, it wouldn't be able to call them anymore because all their names have changed.