Depends on the implementation of the binding. Some devices report their current state periodically whether or not they’ve changed. In those cases, the binding will usually update the Item to indicate that the device reported a new state that happens to be the same as the old state.
There are three distinct events an Item can experience:
Update: a new state was sent to the Item
Changed: an update that resulted in a change in the state of the Item
Commands: an Item was told to do something. A command may or may not result in an update. A command may or may not be the same as an Item’s state (e.g. sending ON to a Dimmer Item could result in that Item changing state to 100).
In the expire config, by setting ignoreStateUpdates to true, you are making it so expire does not reset except for commands or changes and not updates. There is a corresponding ignoreCommands option to have it ignore commands too.