Unions are used when you want to store different types of data in the same 
memory location. They help save memory by allowing multiple variables to 
share the same space.

For example, imagine you have a variable that can hold either an integer, a 
floating-point number, or a character. Instead of using separate variables 
for each type, you can use a union. The union will allocate memory that is
large enough to hold the largest member, and you can then store values of 
different types in that memory.

One common use case for unions is when you need to interpret data in 
different ways. For instance, you might store an integer in a union and then
access the same memory as a floating-point number. This allows you to
manipulate the underlying bits directly.

Another use case is when you have a data structure that needs to be flexible
and hold different types of values at different times. Instead of creating
separate variables for each possible type, you can use a union to store the 
different values in the same memory.

However, it's important to use unions carefully. You need to keep track of
which member of the union is currently valid, as accessing the wrong member
can lead to unexpected results or undefined behavior. Unions are commonly 
used in low-level programming, interfacing with hardware, or situations 
where memory optimization is crucial.