Event scheduler can be used for planning of recurring events. Example: If you are in a small sports club, you could plan weekly games. Members will be able to join or cancel, so other members can see who participates in the game. You can plan vacation schedules, where no events will be scheduled. Last but not least you can notify users that have not accepted or canceled the event yet by email.
In recent Typo3 version 7, the way of handling datetime fields was changed. Datetimes are now converted to UTC before they are stored in the database. A workaround was introduced, that fixes this problem. It might be, that you already have wrong event