Thank you for the question.
When issuing the DEFRAG C: -A-V command,, you get a lot of information, but you can not decide if it is good or bad.
MS are using percentage, but you are not sure of what.
What the user want to know, is whether he is suffering from performance degradation or not.
The figure LAVELEVEL give, is proportional to the performance degradation of the computer, and thus to the satisfaction of the user. It is extremely important in Servers. You may live without it if you decide not to look ant your data's internal structure. Please remember, that copying the disk solves everything!
THIS IS THE FIRST TIME THAT SUCH A FIGURE IS GIVEN.
You may run it, either on a loaded disk or a tidy one, and see it for yourself. Run it before and after the Defrag, and you'll be convienced.
It is the same in SQL. dbcc gives the figures, but if your need a qualitive measurement, you'll have to wait until we'll finish.