It is not universally useful to enfore a single assignment mode. With
short conditionals (or even a ternary operator), an assignment of the
returned value is common. For longer or more complex conditionals, I
perfer an assignment inside the condition to decouple the conditional
checks from the assignment logic.
Unfortuntely, Rubocop is often not smart enough to figure out which
block style is advised in a certain situation. To avoid irritating
false-positives, we just disable this style check.