The best thing you can do for leather is NOTHING.
Leather contains natural oil's that protect it. If/when a spill happens, you should use a damp cloth to clean the spill.
By treating, or conditioning, you are actually removing the natural oils, and sealing the leather, which will in time cause the leather to dry out and crack, especially if you don't continue the constant application of conditioner.
This is especially bad on car's because of the sun, and heat.
That is of course assuming the leather is REAL leather, and not Synthetic leather.
-TheChad