As with D500, D850, D8 etc, the Z9 does allow 4 different setups for Custom Settings (including RSF) besides 4 different Photo Shooting Banks. Obviously, there are 16 combinations to use - if one ever goes that far. In practice, I've found the primary advantage is to have the Landscape Settings (PB D and CB D) ready in a pair of these Shooting banks from the primary wildlife Banks. The option to copy an menu bank of settings is a big jump forward for the Z9 (compared to the DSLR bank designs).
A key Custom option made possible for the Red Record button is another important difference using Zed MILCs, compared to the D850 and D5 (AFAIK the D6 fixes this). I rely on this to switch AF modes with right-hand fingers only. In contrast, it takes only a few thumb-hand clicks in i-Menu (also possible with MyMenu set to a button). A respective pair of PS and CS banks instantly returns to all the settings for its designated Task/Genre (image, shutter and Custom controls etc) cf my attempt to capture the relationships in
Z9 setups in this horrendogram.
I tend to use the pair of PS & CS Banks (both A) most of the time, changing key settings on the fly. Almost all these quick changes are for wildlife subjects. I shoot the Z9 much like my DSLRs. My main reason to switch to Action Settings (PB & CB B) is for different Custom Area configurations. Much wider expanse of CA1 in CS Bank B uses Subject Detection; and RSF [Hold] on Fn3 in CS Bank B drops from 20 to 12fps, and toggles Subject Detection Off
*.
The release of
RSF (Recall Shooting Functions) in D5 firmware 1.30 update (2018) expanded the scope of Custom settings possible for action shooting; and the D6 has taken the scope of RSF further. I've found the settings that work best in practice for wildlife use one's
Right Hand only. True to his style
Canadian Wildlife Pro, Brad Hill, has quite a lot to say about Shooting Banks. There are links to his recent blog posts here.
The RSF on Fn3 is easy to toggle shooting vertical as well as horizontal: especially to toggle Subject Detection Off
*.
*Note: Z9 owners still await the Z9 firmware upgrade to fix the glaring bug - the Custom Settings (f2) option to assign a Function button(s) to toggle Subject Detection Off. This will then free up the scope of RSF for worthier tasks.