The mastering signal path should be kept as short as possible with unneeded gear removed
In professional mastering facilities both analog and digital signal paths are available, but the cardinal rule is to keep the path as short as possible. Any unneeded equipment is removed from the chain so the signal remains unaffected. Every additional piece of electronics can color or degrade the signal. The philosophy is to use only what the material requires.
Examples
Bob Ludwig routes minimal, audiophile Massenburg/Sony electronics designed to be as close to a straight wire as possible, keeping unneeded gear out of the chain.
Assessment
Why do professional mastering engineers avoid inserting gear they are not actively using into the signal chain?