I started sporadically using Day One back in 2014. At first it didn't really feel like it was worth the effort of having to add an entry, but once I had a number of entries and some time had passed its appeal starts to show through.
I mainly use Day One to mark particularly memorable events, usually with a photo. Something I have started to appreciate now that I have hundreds of entries that I can scroll back through.
Day One 2 launched today with a whole host of new features. In a world of free apps, this one is definitely worth paying for.