Final answer:
Common reasons for installing an app from the Salesforce AppExchange include obtaining a pre-built application to address specific business needs and enhancing the platform's standard functionality with additional features and tools.
Step-by-step explanation:
Common cases for installing an app from the Salesforce AppExchange include when a Salesforce user needs a pre-built application to address a specific business problem or when the user requires enhanced functionality beyond what the standard Salesforce platform provides.
(b) A Salesforce user needs a pre-built application to simplify a business issue: AppExchange offers a range of ready-to-use applications that are designed to meet particular business requirements, which can help users to quickly add functionality without the need for extensive customization.
(c) A Salesforce user needs standard functionality to be enhanced: When the out-of-the-box features are not sufficient for unique business needs, a user can turn to AppExchange to find apps that extend or add to the functionality of the Salesforce platform. These enhancements can be in areas such as project management, marketing automation, or analytics.