If someone has 100BTC that they received a week ago and they spend it then 700 bitcoin days have been destroyed. If they take those 100BTC and send them to several addresses and then spend them then although the total transaction volume could be arbitrarily large the number of bitcoindays destroyed is still 700.
If someone had 100BTC for 7 days and send 1 BTC and 99 BTC returned to his wallet as change, how many bitcoindays were destroyed? 7 or 700?
I guess in this case it will be 700, because both coins were moved. But then this indicator still don't count the real meaningful transaction