With only 2 60's onboard and one of those in the D. The other is not being used much due to the way we conduct/train for tactics. You can break this argument down a few different ways. Having a third allows you to work phases, flight time, etc in a much better way. If you have one in Phase then the other is 1 to make 1. That bird goes down and the heat is on the OIC because the ship still needs to meet the SAR matrix. But that is not what we are pushing, just an added benefit.
Using one in the D allows 2 for tactics. Whatever that may be. VBSS, ASUW, 240 or GAU, Hellfire, Rockets, Putting/investigating contacts in the link, streaming live video to the bridge. LHD Dets do a lot of training/HARP for deployment. Day night VBSS, a few trips to MUTC with the teams, workups with the MEU, etc. Then we actually deploy and it is "Here is your D, there are many like it but this one is yours".
We currently have the det on the IWO and will also have the KSG. The IWO det did a great job of starting to integrate with the MEU and pushing that we are more than just a SAR platform. Now it is getting not only the Marines to buy into it but Big Navy. All you need is space for 1 bird and some extra personnel.
No one cares about the 60's till they are both down. Then the sky starts falling.