It's true, but 95% of the cases you get much better results by using the right data structures (dictionaries) instead of transforming queries to loops. Still is a very cool thing, hopefully is standardized into Roslyn
BTW I cover this in my recent book: https://www.packtpub.com/mapt/book/Application%20Development...
You could try code samples and benchmarks: https://github.com/PacktPublishing/ASP.NET-Core-1.0-High-Per...