Because it does not give the correct results.
Whether I pick sum or average as the first aggregation with moving average as the second, the results are much higher than they should be. This is also the case if I set the interval to 3m (my netflow output setting).
With sum and interval set to automatic I get graphs reporting 34MB/s. Interval set to 3m I get over 100MB/s.
With average I get something like 15MB/s and 4MB/s with the interval set to 3m.
It also would be nice if Time series would draw a line between data points instead of leaving it empty, causing gaps. This does not make sense if you set value /s.
The real speed was 1MB/s and the Timelion graph using mvavg does display that correctly.
Making gauges is even harder. I would expect that having the sum of out.bytes with an average of out.bytes (would be overall average and sum of out bytes I suppose) would give me the average speed but it doesn't. Instead it gives a totally unbelievable number that makes no sense.
I don't want to sound negative because I'm sure its mostly me that is the problem and the product and support are great but better documentation is needed. I have no clue what most options do and explanations and examples are thin and spread out.
Every visualization should have a explanation of all options, even if that means you're going to end up with the same explanation 20 times.
I suggest setting up a device that exports netflow and see for yourself. It's the standard in networking. I don't think you'll get good graphs or gauges, at least not in a way that the average user would think of when creating visualizations.
Edit: I don't think its possible to use scripted fields that do work with other visualizations.