I had my DNA tested by Family Tree DNA years ago. I had investigated my paternal ancestors back to Ireland and found the man who emigrated to the US in 1851 - my ggGrandfather - and born in 1829.
But that was as far back as I could go. Stone walled primarily because before the early to mid 1800s, Irish-Catholic documentation was almost non-existent.
So, if I wanted to find other relatives related to me via my ggGrandfather, I had to go the DNA route.
The Catholic parish records are now available online thanks to the National Library of Ireland: registers.nli.ie
Problem is that you need to know the exact parish where your ancestors lived...and the pages are not always easy to read.
I have an Irish ancestor whose date of birth I know, but I don't know where she was born and her surname is a very common one, so I have not managed to locate her yet. Maybe if I spend enough time on it I will find her.