I was asked today, 'Am I correct to think that Databuffers do not return Null/Blank cells and therefore you don't need to check whether the cellstatus is Not NoData?'
The full data unit is in memory and Time is part of that. The system needs it in memory so it can figure out impacts to the whole year. When you can a data unit for a month you are calling only part of the full data unit.
For future period the data will be there, but not in the prior months. If the data was there in Jan, but not Feb - Feb would be derived zero.
Only because period is part of the full data unit, it is possible that you could have a value in Feb, but NoData in Jan. In that case when call the Jan data and buffer only Jan, you might think you have a true No Data. That is why we have the function to check.
Honestly though, if the value existed in Jan, you probably need to run it for Feb too though. Using Is Not NoData should NOT be a default, you decide if you need it or not.