Not entirely accurate. Plant3D does a *lot* more than "just lines on paper". It provides data-rich models which can be coordinated not just with Navisworks but directly XREF'd into other AutoCAD-based products like Civil3D. Only recently has Revit started into PCF and piping isometrics, which have been present in the DWG side for... well, lets just say it's been around a little bit longer.
Plant3D is also spec driven design which is essential in the process piping industry. Not to mention it delivers content directly in DWG format, which is still very common in that industry (hint: the natural gas you're using wasn't processed in Revit-designed facilities). Giving a Revit model to a client in the process piping industry will get a response of "What am I supposed to do with this?", no matter how "BIM" it is.
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If you are going to fly by the seat of your pants, expect friction burns.
"I don't know" is the beginning of knowledge, not the end.