Do you want to see an acutal example or are you looking for ideas of why you would create one and best practices surrounding custom step types?
If you are looking for an example then look in the shipping examples for TestStand under StepTypes. That seems like a great use case as well.
If you want best practices then here's what NI recommends: http://zone.ni.com/devzone/cda/tut/p/id/8300
Personally I've never had a use for custom step types. Although I'm sure there are a few times when it would have made my life easier. I know that back in the day (pre TS 4.0) people used to create custom step types that were already linked to code modules. It made it easier so you didn't have to configure the step each time you needed to call that code module. Now that templates are there this has eliminated that need.
Cheers,
