This is a good default.

Timer · Timer · commit 7cf69bd8bfb7 · 2018-01-12T20:09:17.000-05:00
Adds approx 4 seconds to install time, but can save some headaches.
diff --git a/.yarnrc b/.yarnrc
@@ -1 +1,2 @@
 --install.no-lockfile true
+--install.check-files true
