In P6 R8.3 what is the best summarize setting and why?

We are planning on migrating from P6 v7,5 to P6 R8.3 in 1 week and in creating our procedures a question came up about summarization settings. In our P6 v7 we have been using by calendar and when we apply actuals our last step is storing period financials. Is it better to also have the by financial periods checked as well and what does that give you? I have read the help documentation but I only get more confused. We have been running P6 for 5 years with the by calendar setting and storing period financials and all of our