Final answer:
The Data Loader in Salesforce should be used when the user's org permits Salesforce's API access and when exporting large quantities of data from their Salesforce org. It does not natively support Linux OS or import from XLS files directly, as they must be converted to CSV first.
Step-by-step explanation:
The Data Loader in Salesforce should be used in specific situations. It provides functionalities that are critical for bulk operations on data.It should be used when the user's org edition and settings permit Salesforce's API access. This is important because Data Loader interacts with Salesforce using its API, and without the necessary permissions, Data Loader cannot function.It can be used when a user needs to export large amounts of data from their Salesforce org. Data Loader provides the ability to export data in bulk, which is essential when dealing with large datasets.
While Data Loader can support data imports, XLS files would first need to be converted to a supported format like CSV before they can be imported. Also, Data Loader is a Windows-based application, hence a user on a Linux based operating system would need to find alternative methods such as using the Data Loader command-line interface or a third-party tool.