I hike with the same people on a regular basis. After many trips together, whether for a day hike or a multi-day trip we know what gear each has without having to resort to a checklist. That said, the one and only firm rule is that each person carries at a minimum, their own 10 essentials.

On longer trips, a personal gear list (nothing like forgetting to pack toothpaste) does help but not to the extreme point of showing my partners my gear list....just in case. We share some group gear such as stoves, cookware, shelter etc, other then that I don't really care what my comrades are packing. The expectation is that if you forget something and someone else has extra to spare, you share with them. Of course there are some personal items that you just don't share...