Thanks for describing it like this - it's very clear what you mean now.
Awesome! This technique that you're describing was frequently used by Chet Atkins, Lenny Breau and others in the same style. It is a really great technique that I strongly recommend you to explore! I've used it too, but not enough! :) It's more commonly heard by nylon string players - for instance, I've heard the great Richard Smith use this "p m i"- pattern many times.
Check out this video at 1:42, where Chet Atkins is using the technique in the song "Cascade". There are SO many techniques and ideas to learn from in this video!!
So to answer your question; I'm actually not using this technique a lot since I feel that I can reach the same speed using only alternating between thumb/fingers - and I feel that its easy to get stuck when playing this technique on steel string guitars. On nylon it's much easier for me! But I need more practice! :)
Also, check out the lick at 0:42 in the video above (Chet Atkins playing Cascade), where he's using the "p m i"-technique when playing a descending line (3 notes per string).. It works great on descending lines. He's basically just playing a C major scale from the 3rd of the scale (note E) on the high E string, and playing the scale all the way down to the low A note on the low E string.. :)
Have a great day!
Have a wonderful dat!