Signature Loop

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It’s common for businesses, particularly larger ones, to have a required signature hierarchy. Typically, someone is in the signature loop for one of three reasons:

Add Value
This person is knowledgeable about the issue needing sign off. She is likely to have a perspective that others do not, and likely affects the decision.
Intimidation
This person represents authority and thinks that he provides a filter by making his subordinates seriously consider the items they bring. However, he seldom declines his signature.
Ego
This person is the superior, and thus she should automatically need to sign off on all items below her. For this person, signing off provides egotistical comfort.

Who out of these three categories should be included, and what value are the others truly adding?