Your employees can receive a notification when they are allocated to a new task.
It can help them to become aware of new tasks and make sure that they do not miss any deadlines.
It also ensures that they are aware of a specific project for the time they spent on it, so you make sure that your time registrations end up on the right projects.
You can enable the notification in the System administration -> Project -> E-mail notifications -> Notification: Allocation Created.
Here you must set a checkmark in Active and remember to click Update.
Maybe there are other automatic notifications you can use as well to make the internal communication easier?