I don't know much about leather clothes but I do use 303 on my leather truck seats. There are certain products (very good ones, btw) that "feed" untreated leather such as Leatherique and Lexol. But most modern cars have treated leather. This leather is treated with a vinyl type coating which is there to resist spills, dirt and any kind of absorbtion. While the leather conditioners need to be absorbed by the leather in order for them to do their job, the coating is doing its job by resisting these products, or anything else, from penetrating to the leather itself. Some will get through but a real leather "feeding" will not happen until the protecting coating wears away. This will, if it ever happens, then create a natural leather situation. Some European cars and perhaps some high end American vehicles still have natural leather but most vehicles these days do not.
So, it appears that a product like Protectant 303 (which is approved for leather use) will condition the leather coating which in turns protects the leather. Plus, it has superior UV protection which is very important if you leave the car in the hot sun a lot. This is especially true if you lived in Texas as I do.
I suppose clothes may or may not be treated and a good leather conditioner is the thing to use for untreated leather. One good way to tell is place a drop of water on a small area. If it beads it is coated leather you are working with. If it is absorbed, you have natural, untreated leather.
