Server Side Functions Use Cases

1. use cases must illustrate that a (say) "mean" may be taken over a subset of the coordinate axes for a variable. The mean collapses dimensions of the original grid to produce a degenerate grid result. E.g. an area mean of an lat-lon-time variable produces a time series.
2. application of this: difference time series of the same area mean from two different datasets. Requires these nested operations:
   1. area-average each of the variables over the same (or different) areas
   2. specify the vertical coordinate point on each in a geo-aware manner. (i.e. not by vertical index)
   3. specify the time range; regrid the time series of one variable to match the other
   4. take a difference between the two time series
3. this is an equivalent use case but on different dimensions: difference XY fields from time-averaged results
   1. time-average each of the variables over the same (or different) time ranges
   2. specify the vertical coordinate point on each in a geo-aware manner. (i.e. not by vertical index)
   3. specify the lat-lon range; regrid the lat-lon coordinates of one field to match the other
   4. take a difference between the lat-long fields