Sometimes companies are required to keep part of their data for a certain amount of time. This is often the case when the company is subject to one (or more) regulatory requirements or possibly under investigation.

One way to go about this is to kindly ask users not to delete items from their mailbox or maybe move them into a special container. Using Outlook rules you might even be able to automate part of this task. The problem is that this doesn't ascertain that all data is preserved as it cannot prevent user from accidentally deleting something. It also does not prevent tampering with items or just a user's bad intent. Let's just hope the latter doesn't happen all that often!

In-Place Hold, being a server-side feature, allows for easy preservation of data from one or more mailboxes. Items can be kept indefinitely, based on a query or on a period of time (time-based); all without requiring the user's interaction.