When ball joint boots or tie rod boots tear and don't seal the joint, contaminates such as dirt, grit, water ,etc are introduced to the joint. Grease is a lubricating oil with a thickener being used to hold the lubricating oil in suspension so a torn boot allows the oil to drain out while retaining the thickener which doesn't do much if any lubricating. That causes premature wear of the metal joint and there will be wear of the socket. That brings on failure. Replacing the boot only covers up the eventual problem.