IMO it's situational. Some interiors have vulnerable materials and some don't. Some environments and types of use are more severe than others.
E.g., people have had problems with the dye of their clothes transferring to seating surfaces; some steering wheels have degraded while the identical steering wheel, in other situations, didn't (specifically Audi steering wheels- mine never have problems but when I sold a nearly-new A6 to a friend the steering wheel needed replaced due to flaking/peeling in no time).
I myself hardly ever use Protectants yet I don't have problems. A few exceptions: I do use Leather Doctor's Protectant on the S8 now and then, and I've used it on the A8 once or twice..nice stuff if you do want to protect your leather; I occasonally use Leather Master's stuff on the *VERY* compromised front seats of the Tahoe and that's arrested the degradation just fine (people predicted I'd have to replace the seatcovers ages ago but they're still doing OK).
I honestly can't remember the last time I've used a Protectant on vinyl though, IME today's vinyl doesn't seem to dry out/degrade the way such stuff used to back in the day, but again that's just in *my* experience and YMMV.
Basically I just do quick wipe-clean work with Meguiar's IQD or 1Z CP.
Einszett (1-Z) Cockpit Premium...
I really like that stuff! I use it pretty often, but I sorta wonder how much protection it leaves behind.