The advanced shakedown can be very helpful if your crew is prepared for it and knows their goals. I assume your crew members have read Doug Prosser's excellent article
Our crew members this year got really into going light. We had a competition between the scouts to "Be the Biggest Looser" that went on all year. At every preparation hike we would use a luggage scale to get everyone's newest base weight and announce it to the crew. During the last two months it got really competitive and almost everyone convinced their mom that she needed a digital kitchen scale that measures 1/10 oz.
In their effort to go light the scouts made choices that required them to convince our ranger that they know what they are doing and get the ranger's OK. Here are three examples.
1) No pots, no pans, no frisbee, no spatula, no dishwashing. Our crew had decided to rehydrate the Mountain House meals that Philmont provided for dinner in a quart-size Ziploc bag. After re-hydrating the meal in the Ziploc bag they would pour half of it back into the original Mountain house bag and thus had a bag to eat out for each cook buddy. There was no dishwashing needed afterwards. You just roll up the empty Ziploc and you are done. That saved them a lot of weight and a lot of time they could use for activities. Philmont rules require you to take a "Frisbee" and a spatula to deal with food left overs after dishwashing. Our crew was successful in convincing their ranger that their system didn't need it and he allowed them to leave those items in the locker.
2) No Philmont bearbags. The Philmont bearbags are heavy and require a lot of time to sort through everything over and over again. Our crew members had individual 20 l UL drybags (1.2 oz) in different colors with names written on the bottom. Again the crew would save weight and time. When they hung the bearbags, everyone would just clip their individual bag in and was done. In the morning everyone would just take their bag and put it into their backpack with no time wasted.
3) Tarptents. Several of our crew members used tarptents with polycryo groundsheets (1.6 oz). Philmont requires that the bottom is connected to the tent. That is obviously not the case with a groundsheet. We had brought heavy bathtub floors that could be connected to the BD Beta Light to be compliant if needed. But the ranger was again flexible once he saw that our scouts knew their gear and knew how to use it. My "tent" was a Gatewood Cape.
Our ranger became really interested in our gear choices and the rationale behind it and then started to make additional suggestions that he felt would fit our style - for example to leave the rain pants in the locker.
We had several 14 year old scouts in our crew and going light allowed them to thoroughly enjoy Philmont. They chose to do many extra miles to get to additional activities that were not directly on our trek. In the end they backpacked over 100 miles (which was not a goal, but just happened). I contribute that mostly to the fact that our "biggest looser" had a base weight of 12.2 lbs. Even the "heaviest" member of our crew (an advisor) had a base weight of only 17.9 lbs. These baseweights evolved over many months of preparation (and competition to be "The Biggest Looser"). Our crew had practiced with the gear and knew how to use it and convinced their ranger.
Your advanced shakeout with a ranger can give your crew an opportunity to explain their choices and defend them successfully. It can also provide you with insight in where rangers are flexible. My impression is that it differs a lot and we were lucky to get a very experienced ranger. Some newer rangers seem to go by the book and show less flexibility.