I use several different file managers and have those buttons in that location for all of them... except Salamander.
So I'm just trying to extend my "mouse motor memory" to include Salamander so there isn't that slight hesitation while my hand determines which software I'm in (before moving to a button that normally is in a fixed location but is somewhere else in Salamander).
If possible, I configure all of my toolbars and their buttons to the same locations, no matter the software.
A mixture of the selection buttons
Select all
Select none
Etc.
Focus name in other panel
Open name in other panel
Essentially any button that is about the PANELS should be optional in the panel toolbar. I personally wouldn't put FILE ACTIVITY-related buttons (copy, paste, rename, etc) in the panel toolbars (I use the center bar for those, thanks so much for it!).
But why place artificial restrictions on what a user can place in the panel toolbars? Everyone works differently.
Plus, my monitor is 1920x1280... plenty of room for more buttons.