Keeping machines up to date can be a challenge. Munki tries to make this as seamless as possible, especially if you mark certain items as unattended installs (Munki will try to install those items in the background and not even bother the user).
But some updates require a logout or a reboot, and users generally don't like to log out or reboot often, particularly if they have laptops (as opposed to desktops). So pending updates can sit there for days, weeks, months, even over a year, unless you force the user to install the items.
I wouldn't recommend using the force_install_after_date option very often, but it can be very handy, particularly if there are critical updates that need to get to users.
And even though Munki itself will attempt to notify users of forced updates, you may want to accompany those built-in warnings with warnings of your own (via email, in person, etc.).
At the final countdown, the screenshots below are examples of what your users will see. Every time there's an OK button in the Managed Software Center, your user has the option to close Managed Software Center for a short time, but then MSC will just pop back up again soon. At the very last dialogue, the user will have no choice but to install the pending install item.