Understanding Today function and when it refreshes

Hi LazyUser 

You might refer to the document for what's refreshed in power bi service:

https://docs.microsoft.com/en-us/power-bi/connect-data/refresh-data 

For Composite models, based on my test, We can configure the scheduled refresh on it, the cache of titles will refresh after refresh complete, we can configure maxium 8 times on shared capacity or use on-demand refresh.

furthermore, the advantages and disadvantages associated with Import and DirectQuery, depending on how each table is configured. But it may reduce the size of dataset and duration time of refresh because some table use direct query instead of Import. Please refer to this document about the Composite models: https://docs.microsoft.com/en-us/power-bi/service-dataset-modes-understand#composite-mode