docs: add use cases for always

docs/function/always.mdx

@@ -15,3 +15,19 @@ const alwaysTrue = _.always(true)
 alwaysTrue() // true
 alwaysTrue(1, 2, 3) // true
 ```
+
+### Use cases
+
+You can avoid using `always` if the value is a primitive (use `() => true` instead), but it can be useful if you need a function that always returns the same object reference, or if you want to memoize a calculation across multiple calls.
+
+```ts
+// Not memoized
+() => someCalculation()
+// Memoized
+_.always(someCalculation())
+
+// Not same object
+() => ({ a: 1, b: 2 })
+// Same object
+_.always({ a: 1, b: 2 })
+```