What role does competitor research play in a product-led approach vs. any other approach?

Everything. 

Without being able to differentiate your product in the marketplace, what are you besides just noise? 

Competitive research isn't specific to PLG or any strategy -- it's necessary for any business to survive and properly compete. The "build it, and they will come" strategy doesn't work in the real world. It's about building products/software that people WANT that does a JOB and stands out amongst your competitors. You're not doing this without properly doing research 

Competitor research is critical in both product-led and all other go-to-market motions. It isn’t specific to solely product-led growth (PLG). Especially in today’s market, you need to deeply understand your customers and how you drive value for them versus competitors. You need to understand market trends and how your competitors are responding to these trends. Without competitor research and understanding the landscape, none of this is possible.

While the usage of competitor research may differ, know this is something you’ll need to do on an ongoing basis across all go-to-market motions. Your competitors are constantly evolving so bake in competitor research into your ongoing processes.