When designing an exam, would you mention the maximum score per question or not? Is it common practice? 

In my view this promotes cherry-picking. This could be seen as a way to prioritize or to satisfice (leaving questions open since "they are not worth it"). 

Is there any scientific proof/pedagogical insight this is a "must", "nice for students " or "making it easier for students"?

Any thoughts on this (from professors and students)?