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Lists evaluate operations eagerly — each step produces a new intermediate list. For large data or chains where you only need part of the result, that's wasteful.

Sequence is the lazy counterpart: nothing runs until a terminal operation (toList, sum, find, count, etc.).

// Eager — creates an intermediate list at each step
val result = (1..1_000_000)
    .map { it * it }
    .filter { it % 7 == 0 }
    .take(5)

// Lazy — pulls only what's needed for take(5)
val lazy = (1..1_000_000).asSequence()
    .map { it * it }
    .filter { it % 7 == 0 }
    .take(5)
    .toList()    // forces evaluation

For short chains and small collections, List is fine. For long pipelines or huge sources (or infinite sources via generateSequence), reach for Sequence. Same API — just .asSequence() to switch in.