What Are Effective and Expiration Dates?

Any item in the Plone system can have effective and expiration dates if the person editing the content wants. Both of these are optional, and leaving the fields blank will ensure that these values aren't set.
One example of an item that may have an effective date is a press release. In the ideal world, the news item is crafted, prepared, and reviewed in Plone. However, suppose the news item has to go live on the Web site at midnight, but that's exactly when you plan to be sleeping.
Not a problem—give the press release an effective date and a time of midnight. Up until the effective date, it won't be visible in the calendar, in navigation, in searches, or in pages that use a search as the listing under the news tab. However, anybody who knows about the press release will be able to access the page directly. Once the effective date has passed, the item will appear in all the aforementioned places and be live to the world.

The effect is similar with expiration dates. If you have a special offer that stops being effective on a particular day, then you could set an expiration date of that day. After that, date it wouldn't appear in calendar, navigation, searches, and so on.

The effective and expiration dates don't actually change the state of the item in workflow rather, they just change where it displays.