I see the postings stating that most car leather these days is top coated (apparently urethane paint) leather so traditional leather conditioners should not be used and of course most cars (those under 50k) with leather sets only have leather in the seating area (leather trimmed seats) so those that use a conditioner elsewhere are applying it to vinyl.
However, most of the recent leather conditioners (like Lexol) aimed for the car market seem to be synthetic (not natural mink oil or whatever, etc) and more akin to a lotion rather than an oil. I asked Lexol directly and they said that a conditioner will not harm top coated leather and as it ages it can benefit from a conditioner since it is not like paint on a car surface. Of course, they have an interest in stating this.
The part I find interesting is that if applying a conditioner on top coated leather is a waste of time I wonder why so many people who do claim it softens the leather, etc. Most do not claim it leaves them greasy. I still think something is missing in this technical debate.