The leather in our Audis and GMs is very different from the leather in the Jag and I assume that's the difference between "modern" and other leathers.
The Jag's leather dries out and becomes very stiff and prone to damage if I don't use "conditioning" products, which it soaks up like a sponge (leaving no residue behind once I've buffed off the excess). The leather in the '97 BMW is sorta in-between, and it does seem to benefit from conditioning, getting softer and more flexible ("better") with treatment. If I didn't condition these leathers they'd crack and suffer damage at the seams- the Jag having already suffered some (thankfully minor) damage of this type when it was *not* conditioned for a somewhat extended period

No problems with residual product or dirt attraction/retention, no product transfer when wiped with a white cotton cloth, at least not by the time I'm finished (no product residue on *our* clothes thank you

).
The Audis on the other hand, do not seem to need any conditioning and I usually just keep them clean. In 7-8 years of ownership, I've conditioned (using water-based products) the S8's leather once since new and the A8's three times...never noticed any huge difference when I did it so I haven't stuck with it. Haven't had the GMs long enough to even think about treating the leather, again, I just keep 'em clean and they seem fine.
I've inspected a few cars of various vintages that were treated with Leatherique's Rejuvenating Oil; the oil did not leave any sort of film/etc. on the surface of the leather but rather rendered it soft and pliable without over-conditioning it (which I do recognize as a potential problem, having experienced it with non-automotive leather goods). I haven't gotten around to trying mine yet, but I bought it based on first-hand inspection of what it can do...some day we'll see how it works on the Jag.
I sure don't want to :argue with a leather specialist like
judyb but my first-hand experiences/observations are hard for me to dismiss. Again, it could well be the nature of the leathers involved and my experiences with the Audis and the GMs sure do fall in line with what she's posted.