My use case was--> referenced a void method in the action attribute on an apex:page In the void method, check for a condition. if true, do nothing, else call a pagereference method to redirect to another page.
I tried using a void method here since the general opinion seems to be that using a pagereference method and returning null is bad programming.
But this didnt work, the page never redirected when expected. The same logic with a pagereference returning null works fine.