Tuples should be used when we need to store an ordered sequence of elements that should not be modified. Since tuples are immutable, we cannot change their elements once created. This makes them suitable for storing fixed data like days of the week, coordinates of a point, or storing email IDs of students where data integrity is important. For example, a program can store student email IDs in a tuple to ensure they remain unchanged during processing. Tuples are also useful when we want to return more than one value from a function.

Dictionaries should be used when we need a mapping between keys and values. A dictionary is an unordered collection of key-value pairs enclosed in curly braces. They are ideal for situations requiring quick lookup of values based on unique keys. For example, a dictionary can store state capitals like stateCapital = {"Bihar": "Patna", "Rajasthan": "Jaipur"} where we can easily find the capital of a state using the state name as the key. Dictionaries are mutable, so we can add, modify, or delete key-value pairs as needed.

In summary, use tuples for ordered, immutable data, and dictionaries for key-value mappings requiring flexibility.