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kotlinlang

What this "some overhead" is?

So, the sequences let you avoid building results of intermediate steps, therefore improving the performance of the whole collection processing chain. However, the lazy nature of sequences adds *some overhead* which may be significant when processing smaller collections or doing simpler computations. Hence, you should consider both Sequence and Iterable and decide which one is better for your case.

<https://kotlinlang.org/docs/sequences.html#construct>

I believe it is referring to the fact that sequence functions are not inlined.  So the lambdas used have to be converted to actual objects and function calls will actually be made.