This means the storage location of the messages you are supposed to receive could change often, making retrieving messages a two step process, looking up the current online location and then retrieving messages. The place to lookup messages is fixed in a centralized system, hence you'll receive messages faster.
This can definitely be sped up by increasing the number of times the messages are replicated in the decentralized system and a constant shuffling of the message between nodes to ensure it is always available for the receiver when they come online, hence inefficient.