This is very noticable if you have unsigned big integers representing what should be very distinct values (the last N digits are replaced with 0). This makes it nearly impossible to take data extrapolated from Tableau, and cross reference it back to the database, or use these numbers in other meaningful ways.
I suspect this is also an issue for doubles of high precision.
This has been posted as a question with no response here. Luckily some digging and time with tech support has narrowed down it being a "bug" even if documentation wants to pass it off as a warning.