Class action lawsuits may offer a number of advantages because they aggregate a large number of individualized claims into one representational lawsuit.
First, aggregation may increase the efficiency of the legal process, and lower the costs of litigation. In cases with common questions of law and fact, aggregation of claims into a class action may avoid the necessity of repeating "days of the same witnesses, exhibits and issues from trial to trial." Jenkins v. Raymark Indus., Inc., 782 F.2d 468, 473 (5th Cir. 1986) (granting certification of a class action involving asbestos).
Second, a class action overcomes "the problem that small recoveries do not provide the incentive for any individual to bring a solo action prosecuting his or her rights." Amchem Prods., Inc. v. Windsor, 521 U.S. 591, 617 (1997) (quoting Mace v. Van Ru Credit Corp., 109 F.3d 388, 344 (7th Cir. 1997)). "A class action solves this problem by aggregating the relatively paltry potential recoveries into something worth someone’s (usually an attorney’s) labor." Amchem Prods., Inc., 521 U.S. at 617 (quoting Mace, 109 F.3d at 344). In other words, a class action ensures that a defendant who engages in widespread harm -- but does so minimally against each individual plaintiff -- must compensate those individuals for their injuries. For example, thousands of shareholders of a public company may have losses too small to justify separate lawsuits, but a class action can be brought efficiently on behalf of all shareholders. Perhaps even more important than compensation is that class treatment of claims may be the only way to impose the costs of wrongdoing on the wrongdoer, thereby deterring future wrongdoing.
Third, in "limited fund" cases, a class action ensures that all plaintiffs receive relief and that early-filing plaintiffs do not raid the fund (i.e., the defendant) of all its assets before other plaintiffs may be compensated. See Ortiz v. Fibreboard Corp., 527 U.S. 815 (1999). A class action in such a situation centralizes all claims into one venue where a court can equitably divide the assets amongst all the plaintiffs if they win the case.
Finally, a class action avoids the situation where different court rulings could create "incompatible standards" of conduct for the defendant to follow. For example, a court might certify a case for class treatment where a number of individual bond-holders sue to determine whether they may convert their bonds to common stock. Refusing to litigate the case in one trial could result in different outcomes and inconsistent standards of conduct for the defendant corporation. Thus, courts will generally allow a class action in such a situation. See, e.g., Van Gemert v. Boeing Co., 259 F. Supp. 125 (S.D.N.Y. 1966).
Whether a class action is superior to individual litigation depends on the case. The Advisory Committee Note to Rule 23, for example, states that mass torts are ordinarily "not appropriate" for class treatment. Class treatment generally does little to improve the efficiency of a mass tort because the claims almost always involve individualized issues of law and fact that will have to be re-tried on an individual basis. See Castano v. Am. Tobacco Co., 84 F.3d 734 (5th Cir. 1996) (rejecting nationwide class action against tobacco companies). Mass torts also involve high individual damage awards; thus, the absence of class treatment will not impede the ability of individual claimants to seek justice. See id. Other cases, however, may be more conducive to class treatment.
The preamble to the Class Action Fairness Act of 2005, passed by the United States Congress, found:
Class-action lawsuits are an important and valuable part of the legal system when they permit the fair and efficient resolution of legitimate claims of numerous parties by allowing the claims to be aggregated into a single action against a defendant that has allegedly caused harm.
 Criticisms of class actions
There are several criticisms of class action lawsuits. The preamble to the Class Action Fairness Act stated that class actions harmed class members with legitimate claims and defendants that have acted responsibly; adversely affected interstate commerce; and undermined public respect for the country's judicial system.
Class members often receive little or no benefit from class actions. Examples cited for this include large fees for the attorneys, while leaving class members with coupons or other awards of little or no value; unjustified awards are made to certain plaintiffs at the expense of other class members; and confusing notices are published that prevent class members from being able to fully understand and effectively exercise their rights.
For example, in the United States, class lawsuits sometimes bind all class members with a low settlement. These "coupon settlements" (which usually allow the plaintiffs to receive minimal benefit such as a small check or a coupon for future services or products with the defendant company) are a way for a defendant to forestall major liability by precluding a large number of people from litigating their claims separately, to recover reasonable compensation for the damages. However, existing law requires judicial approval of settlement and class members may opt out of settlements.