Reminder generation can be triggered manually or by using a scheduled task here. Unlike generating them manually, with a scheduled task you can configure what types of notifications are generated. Use this, for example, to send out birthday e-mails once per week but assignment reminders every few hours.
Remember that generating reminders is not the same as delivering them. Reminders are letters, and letters must be delivered using the Standalone E-mail Robot, the E-mail Robot (MAPI or SMTP) or the SMS Robot. You can also deliver E-mail notifications using the Scheduled E-mail Delivery task.