doc: clarify writable.cork method

doc/api/stream.md

@@ -358,11 +358,12 @@ The `writable.cork()` method forces all written data to be buffered in memory.
 The buffered data will be flushed when either the [`stream.uncork()`][] or
 [`stream.end()`][stream-end] methods are called.
 
-The primary intent of `writable.cork()` is to avoid a situation where writing
-many small chunks of data to a stream do not cause a backup in the internal
-buffer that would have an adverse impact on performance. In such situations,
-implementations that implement the `writable._writev()` method can perform
-buffered writes in a more optimized manner.
+The primary intent of `writable.cork()` is to accommodate a situation in which
+it is more performant to write several small chunks to the internal buffer
+rather than drain them immediately to the underlying destination. Such
+buffering typically degrades performance, but where memory needs have been
+carefully considered, implementations that implement the `writable._writev()`
+method can perform buffered writes in a more optimized manner.
 
 See also: [`writable.uncork()`][].