Variety of 2 minute, 5 minute, and ten minute poses. There's the challenge of getting the impression of the posture onto the page in the 2 minute versions (often run out of time and leave the head or an arm missing)...and when it comes to 10 or 20 minute poses, there's the temptation to overwork details (creating an unerasable muddy blob).
Sometimes the 5 minute poses churn out a perfect blend of fresh & selectively-detailed! Sometimes not. That's the point of regular practice at anything, I suppose.