The DOE issued a report in 2009 that said, in part, "A thin-client device uses only a fraction of the energy consumed by a standard desktop, results in acquisition and disposal savings, and enhances cyber security."
Thin Clients are inherently secure because there is no data at all stored on the client. Someone who grabs a Thin Client and bolts out of the building will end up with just the hardware. The Thin Client won't even be useful without a Terminal Server.
The typical industrial user is a special case, and therefore does not fit into the Terminal Server sizing requirements usually advertised by Microsoft. This article discusses some of the factors associated with most industrial applications that may make them unique.