Self disembarking is done before normal disembarkation to enable those passengers wanting an early departure and willing to handle their own luggage to achieve it. If you dont need an early departure, but still prefer to carry your own luggage, then I am sure P&O will be happy for you to do just that. But dont expect them to provide a queue free line for you, you would have to patiently wait in the queues, which can slow you down, quite significantly.