What does the "Always execute the script" check box in the "Configure Hook Scripts" dialog mean?

In the Hook Scripts section of the Settings of TortoiseSVN (version 1.9.2, on Windows 7 x64), there is a checkbox "Always execute the script" in the "Configure Hook Scripts" dialog:

The same checkbox is also present in the Properties dialog for "Local hook scripts".

What is the exact meaning of that?
In what situations is a hook script not executed unless this checkbox is ticked?

In the help documentation it is not mentioned at all, the snapshots do even not show that checkbox.

The only thing I found out so far is:
It does definitely not suppress the "Approve or reject client-side hook script" prompt.

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