Slip sliding away
Silicones are the basis for many car care items and the interior is not an exception. In fact, the biggest seller of interior care uses it as the major ingredient in their interior care system. Why you ask? Think $$$$... It's bloody cheap.
Again, not ideal for leather in the same way oils aren't; they seal the surface, drying the leather out and even worse, they make it slippery, something I personally don't enjoy in any car. Silicone also helps attract dust, make it artificially shiny (losing that beautiful, natural leather sheen) and can help bring on cracks in polyurethane coated surfaces as it builds up with each coat you apply.
A lot of the ones that use this in them say they are good for all interior surfaces. Be wary of ANY product that says it can be used on both leather and vinyl, as vinyl is a different covering material and needs an entirely different product formula to effectively clean and protect it from the elements. Most cheap leather care products tend to use silicones or our next beauty of an ingredient...