The class constructor is used to initialize the object, safely and completely, and can also be used to instantiate any compound objects you need to couple in your object. Besides that, I don't see anything you can't do on a constructor.

Update: After seeing your update, the difference from perltoot and WWW::Mechanize::new was the way its doing things. There are not a default idiom to construct your objects. You can do the way you feel comfortable to.