I don't particularly like to do "explicit teaching" (Very structured teaching with an exact learning outcome) with my young children as I believe that forcing this style of learning upon them when they're not ready, or not interested, is not going to help in their future development or for their love of learning.
Any explicit teaching and learning that we do at home comes from my child's interests and almost all of their learning comes from real life experiences and play.
The reason we did this activity was because of my daughter's sudden interest in specific letters. Some things come about naturally, like knowing that "M" is for Madeline, but now she is interested in all other letters and is always asking what their names are and what certain words start with. This is how I knew she was ready.