When to run Lot Cost Process in Final mode?

Not sure if this post belongs in the Cost Management or Process Manufacturing communites, but here goes.

We're implementing OPM and have chosen lot costing as the cost method, and the alternate is Actual costing.  When should the lot costing process be ran in Final mode? 

The way I understand it, no accounting entries can be transferred until the transactions have been final costed.  Is that true?  If so, it would seem that the only time to run in final mode is at period end.  Please confirm my understanding.

Thanks,

JB