Sometimes vs. On Request Pads on Sink Side of Plugin

[Greg Wunder]

I could not easily find a plug-in that uses a sometimes pad on the sink side.
The closest thing I could find were plug-ins like videomixer or mvemux that use "on request" pads (with & without collections).
Is there an example of a plug-in with a sometimes pad on the sink side or is this not proper practice in plug-in development or has it just not been tested/done yet?

Greg
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