I read somewhere (can't remember where) that Airbnb had a dedicated team of 13 engineers and designers working on the welcome email alone. Getting the CTA "just right" resulted in a huge difference in conversions.
So if you’re designing your own CTA, just copy Wal-Mart’s or Amazon’s or Airbnb’s and voila.
In a way, I wish I got to work at Wal-Mart or McDonalds just to get a 1st-Hand view of their processes. Would beat any “LEAN” course.
When I was contracting I was always surprised how outwardly similar businesses could have vastly different IT functions. Sometimes an order of magnitude larger for no apparent gain.