I think it depends on the products you use, as well. What you SHOULD do is contact the manufacturer of your tack and ask what the care instructions are. (but who really does that?) Washing too often can wear down the leather, and oiling too often can wear down the stitching. The quality of the leather and stitching will make a difference, too. At a minimum, I always wipe down my tack with an all-purpose leather cleaner and wipe down the bit after every ride to remove surface dust and grime that can cause sores on my horse. In the summer, I try not to use saddle pads more than twice before washing, so I have a collection of pads to use. As someone else said, it's important to clean regularly so that you can examine your tack for cracks or pieces that may need replacement.