In the book Tea & Etiquette by Dorothea Johnson, she writes:
"Tea strainers are designed to be held above or to rest on top of the cup to catch leaves that escape from the teapot when the tea is poured. I still use one, even though I don't need to since the leaves are contained in my tea filter. It's the ritual of holding that little silver object over the cup, and the pouring of tea into it, that forces me to slow down and enjoy the whole process."
I can appreciate that this action "forces" her to "slow down and enjoy the whole process" but .... I was actually quite dumbfounded by her revelation.
Would (or do) you use a tea strainer when there are no loose leaves in the teapot?