Nobody likes to get sued. It can be an expensive and soul-draining proposition, even if you win. Under the so-called “American Rule,” litigants are responsible for paying their own legal fees, regardless of which party wins the case. Obviously, this system engenders some abuse, as crafty, litigious plaintiffs can file frivolous lawsuits knowing that–at the very least–they will cause the defendant to incur large sums of attorneys’ fees. As a defendant in American litigation, a victory at trial merely means you don’t have to pay the plaintiff any money. But you do you have to pay your own attorneys for their time and effort. So even a “win” is often viewed as a net loss in financial terms. One common way to turn the tables on plaintiffs is to file a counterclaim. Assuming the counterclaim itself isn’t completely groundless, it can put the parties on equal footing: if both parties have claims against the other, then both parties have something to lose beyond mere legal fees. Now, even the plaintiff can be liable for a money judgment.
If you file a counterclaim, however, you better mean it. The court may not allow you to withdraw it later if you decide your claims should have been brought as a separate action in a different jurisdiction. If the case has progressed to the point where trial is imminent, you may be forced to litigate the claim or lose it forever.