When are "db cleanup operations" necessary?

Question

admin-}Stats . recount posts (why / when would counts ever be incorrect?) . reindex content (apparently not the same as "optimize tables", so what / why / when to use it?) recalculate user points (only necessary after posts have been hidden or deleted?) refill event streams (again, when / why is it necessary to perform this 'cleanup' task?)

Comments

that was typed as a "list". Wordwrap editor mangled it. I tried editing to fix -- no dice.

Answer 1

It should never be necessary, but it's there just in case the database gets partially corrupted. The point is that the database contains quite a lot of redundant information, that is calculated from other database information (e.g. the index for searching). All of these types of information can be recalculated from their original source.

Answer 2

As gidgreen says it shouldn't really be necessary. However you need to do it if any time you manually edit or delete something in the database.

In general there is never a need to do that, but there may be occasional situations, e.g. before now I've removed votes that people gave to themselves from duplicate accounts, and needed to redo the points calculations.