Working on a “welcome” email for one of our ongoing migration projects. I've always seen these as unnecessary, from my limited viewpoint and personal anti-automated-email bias. But over the years I've heard from a few people that expected to get an email like this after signing up — if anything, just to remember their username, and that they created an account in the first place.
Now that I'm implementing it and writing the email in the helpful way I would love to see as the receiver, I'm coming around to the idea. We'll roll it out for some very specific signups in the near term, and then expand it to all new signups if it works out well.