If failure to certify class would create a risk of adjudications with respect to individual class members that would impair or impede the ability of other class members to protect their interests.
Typically when litigation is over money in a limited fund that is not enough to satisfy claims of all class members.
Rule 23(b)(2) Requirements of Class Action
Certification of class permitted where class opponent has acted or refused to act
on grounds that apply generally to the class,
so that final injunctive relief is appropriate respecting the class as a whole.
Requirements of 23(b)(3) of Class Action
Permits certification of class where:
1. Common issues predominate over individual issues
2. AND, the class action device is the superior means of adjudicating the controversy.