diff --git a/README.md b/README.md
index 62140e1..da500cf 100644
--- a/README.md
+++ b/README.md
@@ -68,7 +68,7 @@ Options
  * -P: Use multiple threads to read different parts of each input file at once.
    This will only work if the input is line-delimited JSON with each Feature on its
    own line, because it knows nothing of the top-level structure around the Features.
-   In addition, it only works if the input is a named file that can be mapped into memory
+   Performance will be better if the input is a named file that can be mapped into memory
    rather than a stream that can only be read sequentially.
 
 ### Zoom levels and resolution
diff --git a/man/tippecanoe.1 b/man/tippecanoe.1
index 765a740..15c0a9e 100644
--- a/man/tippecanoe.1
+++ b/man/tippecanoe.1
@@ -74,7 +74,7 @@ specified, the files are all merged into the single named layer.
 \-P: Use multiple threads to read different parts of each input file at once.
 This will only work if the input is line\-delimited JSON with each Feature on its
 own line, because it knows nothing of the top\-level structure around the Features.
-In addition, it only works if the input is a named file that can be mapped into memory
+Performance will be better if the input is a named file that can be mapped into memory
 rather than a stream that can only be read sequentially.
 .RE
 .SS Zoom levels and resolution