When would you use a Cache Block, and what are the risks?

Caching is the cheapest performance win available and the easiest way to ship a subtle data bug.

1. Good candidates: reference data, configuration, product catalogues, lookup lists, anything expensive to retrieve that changes on a schedule rather than continuously.
2. Bad candidates: anything user-specific held at a shared scope, anything transactional, and anything the user has just changed and expects to see reflected.
3. Scope matters as much as duration. Caching a personalised result at a global scope leaks one user's data to another — the most serious mistake available here. Match the scope to how the data varies.
4. Set the duration from the data's real change frequency, not from a default. A one-hour cache on data updated nightly is conservative; the same duration on pricing that changes intraday is a defect.
5. Plan for invalidation. If the business needs an urgent change to take effect immediately, know how the cache is cleared before you are asked in production.