Why is controlling concurrent logins to a Windows network so important?

There is no way in Windows to limit a given user account from only logging on at one computer at a time.

In terms of interactive logins at desktops and laptops, a system administrator cannot prevent a given user from going up to one computer, logging on there, letting somebody work as him or just leaving the computer unattended, and then walking up to another computer and logging on there.

And this creates a whole accountability and non-repudiation issue.

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