> This is useful in financial services where you have market data baked into a price you've offered to a client, where the underlying market data might have been later corrected by a vendor.
A long time ago, I worked on a such a system that provided service-based billing for an industry where rates were very fluid. Having this "at any point in time" view of key data was essential for many things.
It allows you to query a system (some databases support this) in a temporal context. This is useful in financial services where you have market data baked into a price you've offered to a client, where the underlying market data might have been later corrected by a vendor.
So you can query how the world looked last tuesday 4pm; but also - given what we now know, how ought the world have looked last tuesday 4pm.
Interesting stuff.