Clients don't care about the contents in my camera bag, just that I show up prepared and insured. (most never question either, though venue owners should). I answer their questions and tell them anything relevant. I went to two weddings as a guest and observed these two photographers at one of the events. They seemed to be tunnel-visioned and neither one of them even noticed an adorable toddler protruding into the aisle quietly observing and eating a snack. If the couple got what they wanted, it's a win. The other, the photographer was barely noticeable but still worked. That couple also got what they wanted. I can't say that I saw the value of the second shooter in the first wedding, though different approaches can create a different result.
It's only a perk if the qualifications and style are similar to the primary photographer, which is not usually the case. I've seen many posts on local wedding photographer social media groups looking for a second shooter at the eleventh hour because theirs bailed. That's just heaping in a second shooter, and it's only because it was promised, and for optics. How is this an asset to the couple? An author writes a book, and a copy editor proofs it. There's one film producer. Are second photographers beneficial to some photographers? Yes. Are second photographers necessary for all wedding photographers? No. Just be sold on your choice for the right reasons.
Overall, for me, it would be unnecessary and redundant. The style consistency wouldn't be there, and the second photographer would infringe on the non-intrusive approach. For those spending more time on posed photos, it makes better sense.