For close family I like to send them a video on their birthday of my daughter singing "Happy Birthday". I found out recently I missed one last year. I decided I wanted to set up Reminders for each of these to go off every year on their birthday so I don't miss one again. Yes, I know their birthdays show in the Calendar but this isn't the kind of thing I want to use that for. I live in Reminders so that's what I went with. However, manually setting all of these would be annoying so I figured I could probably do it with Workflow, even though this isn't one I'll likely use in the future and probably won't even keep in my main workflows. (though I may keep an archived file of it).
My initial approach had me trying to Find Contacts where a birthday was included, but I couldn't figure out how to get it to search the entire year. Every time I tried it wouldn't find anything. Then it dawned on me that I actually have some contact groups set up (which I manage in an app called Interact). It's simple to modify the workflow to search for those groups.
I then used the Repeat with Each action. I then filled in the Reminders section with the name and birthdate pulled from this list (I used a custom date of MMM dd to only pull the month and day.) However here is where I ran into my second issue. I couldn't find a way to set a recurring reminder and I didn't want to have to manually edit each one to make them repeat yearly.
I do have another app which syncs with Apple's EventKit, Fantastical (iPhone/iPad). Lots of people prefer this app, but I mainly use it for it's automation features. In this case, Workflow has a Add Reminder via Fantastical action which can take a string of text, written in natural language, as input and turn it into a reminder.
So I made a text box which looks like this, and pass that into Fantastical.
Like I said, this isn't a Workflow I need to use on anything resembling a normal basis, but even factoring in the two issues that slowed me down, I still think it was faster than manually doing it. Plus it was more fun.