One of the biggest challenges when doing yoga is to maintain ease in a yoga pose - especially when the pose is being held for a long time. The question is: Is it really better to hold a pose (especially one requiring strength) if it, after a certain point, it is only causing tension and stress in the body?
When doing home yoga, it's a lot easier to back off when the body's limits are hit, but when we are in yoga class, the tendency is to want to keep going due to the perceived peer pressure. We don't want to look like a "yoga wimp" in front of others. Yet, perhaps the best yoga is to back off, and those that do may express a greater mastery of "yoga" as a philosophy than those that keep going despite the extreme stress their body is under.
The next time you are in yoga class, try taking a break earlier than normal and see what it brings up for you.