Whether it's your boots, a bag, a jacket or even a vintage club chair, proper care will prolong the life of your leather. The natural fibers will eventually break down with time, so some maintenance is necessary. Think of leather like your skin—for your face to look its best, you've got to clean it up now and again and keep it hydrated. Your leather jacket isn't really that different.
Liquid oils will likely darken leather a little, while pastes often contain waxes and water repellants to dilute the pure oil, thus softening its effect. Remember, don't be afraid of it. Leather is tough, and there's no need to go easy with cotton balls or Q-tips. Use a rag for oils, and your hands for pastes. Work the product into the leather per the instructions (usually 2-3 coats and then let dry overnight). Retreat every 6 months with a single coat, or when the leather feels dry.
When you have new leather soles, you should avoid puddles and rainy days, at least until the soles are well scuffed. Should you encounter a little liquid, you should let your soles dry naturally, so that the layers of leather don't separate. If you get salt on them, wash it off with a damp cloth. You needn't polish or condition your soles, unless you're planning on kneeling in front of a crowd.