Any time you want to store information to be found again later. The information is stored as it is structured: lists, trees, items in multiple lists, and items linked together, e.g. Fred account manager → Barney. Be authoritative with all your information at your fingertips. Sɪᴀ can handle tens of thousands of items, that is hundreds of thousands of words. Sɪᴀ is great for brainstorming and requirements gathering, you can not run out of space. It is also good for mapping out any complex system such as networked software.