Tasks vs Reminders: which to use when

Tasks

Use a task for one-off or ad hoc pieces of work that need to be tracked to completion — comments, subtasks, and attachments make them good for collaborative follow-up.

Reminders

Use a reminder for anything that recurs on a schedule — servicing, renewals, checks — especially where a form should be completed each time it comes due.

In short: tasks are for "get this done", reminders are for "make sure this keeps happening on time".