In common law, a crossclaim is a demand made in a pleading that is filed against a party which is on the "same side" of the lawsuit.
In the federal rules, a crossclaim is proper if it relates to a matter of the original jurisdiction.
Crossclaims, like joinder generally, can promote efficient, consistent resolutions of disputes by permitting all claims arising from the same set of facts to be resolved in a single legal proceeding.
This conserves the resources of the parties and the courts, by requiring fewer cases to be filed and litigated.
It also reduces the risk of inconsistent results that can arise when multiple actions are based on the same or similar facts.