Some polishes, such as paste shoe polishes, contain colorants dispersed in wax that can be buffed to a high shine. Use these polishes sparingly as they can rub off on your clothes or horse. So you need to remove them before a conditioner can penetrate the leather. Silicone based polishes can dry leather out over time and can make leather slippery to sit on. To save both your leather and elbow grease, try an acrylic-based product like Leather Therapy Finish that adds lustre and lightly seals the leather surface while still allowing it to breath and absorb conditioner.
Moisture barriers prevent excess rain or puddles from sluicing conditioning oils out of leather.
When that happens, leather dries stiff or spotted. Paste products based on animals fats like lanolin or mink oil are rubbed in to fill the leather's pores and form a water barrier. They should not be used on napped leathers like suede or nubuck because they lay down the surface fibers. They also leave a greasy residue that makes it difficult to polish smooth leather again and can attract dirt. Spray on water barrier formulas containing silicone can, again, dry leather out over time.