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Usage of System Variables

A colleague and I were having a discussion recently about system
variables in IDL. My colleague regularly uses system variables such as
!p.region, !p.font, !p.margin for configuring plots. My opinion is that
system variables should be used as little as possible. In fact the only
system variable I ever modify is !p.multi for creating multiple plots.
Otherwise I prefer to use keywords to plot, surface, tv, tvscl, etc.

It seems to me that modifying global system variables is not a good
idea, since they have a global effect. These days you can write
applications which run while leaving the IDL command line active, and
setting/modifying system variables in this case sounds like a recipe for

Can anyone think of other cases where setting a system variable is the
only way to achieve the desired effect (e.g. !p.multi)?


Liam E. Gumley
Space Science and Engineering Center, UW-Madison