A class should have only one reason to change.
When a class has more than one responsibility, then it is going to have more than one area to change. Moreover multiple responsibilities become tightly coupled. Changing one can affect the other. Modifying code for different reasons also increases the possibility of having more bugs in the code.
Another general concept closely related to Single Responsibility Principle is Cohesion. A high cohesive class has a set of related functions, where as a low cohesive class has a set of unrelated functions. A high cohesive class is more maintainable than a low cohesive one.
Cohesion is used as a measure of how closely a class or a module supports a Single Responsibility Principle.