Redlining can be used for various reasons but is most commonly used to identify areas of disagreement so that the parties can focus their negotiation on those specific points. It can also ensure that all contract changes are documented and agreed upon by both parties. There is no set rule for when contract redlining is required, but it is often done when there are significant disagreements between the parties on the contract's terms. If both parties can agree on the vast majority of the contract's terms, redlining may not be necessary. However, if there are several key points that the parties cannot agree on, then redlining can be a helpful way to narrow down the areas of disagreement and focus on the negotiation process.