Stage Table for Fact Data

Is it a best practice to truncate a stage table before every load?

--- RPC

In general, yes. Just make sure you have a mechanism to recover old data if a load went bad, or if you accidently start a new load when you should not. For example, you could have a step at the end of a load process that streams the staged data to a text file that is zipped and archived. Or, if your initial source is a flat file, zip and archive it so it can be recovered at a later date.