Require Vault Password

Entries for logins have an optional checkbox marked "require vault password".
I understand that if this box is checked, it forces the user to supply the vault master password before auto fill of credentials is allowed to occur. What is the actual purpose of this requirement, and what is the disadvantage of not checking this checkbox?
To gain access to this login credential information, the user has already been required to enter the vault password, just to be able to open the vault in the first place. To have to enter the password again each time an autofill is required is cumbersome, does not appear to serve any known useful purpose, and the advantage of doing so is not clear! Please explain the reasoning behind the use of this checkbox, and in particular the disadvantages of not checking the box.