Table buffering and also CDS view buffering should be used for data that is only rarely changed, and also the amount of data buffered should not be too huge. Typically, customizing and organizational data should be buffered, and also small / medium sized master data can be buffered.
Data that is buffered in the table/CDS view buffer normally should not be cached redundantly by the application in internal tables (an exception can be small data sets that are accessed with very high frequency).
ABAP application buffering on the other hand makes sense for data specific for the current transaction. But in times of stateless programming, it is becoming difficult to implement an application buffer.
