Sometimes in yoga we'll hold a pose for longer than we may normally want to because the teacher has asked us and has set it up that way. For example, a class might be asked to hold the Pigeon pose for a while or a Bridge pose. More intense might be to hold Warrior or Mountain. What happens is that we get to a place that we call an edge and then we hang out there. If we go over the edge the pose collapses and we're done and if we don't make it to the edge we're not really doing that exercise then...
One of the things that exercise does is gives us practice and some experience at being at the edge so that when we come to the edge in our lives, we have an idea of how to handle it. We can breathe through it and know it will be over soon - it will pass. It's not a great way to live all the time, but sometimes we're at the edge and we need to know how to handle it when we're there. Kind of like defensive driving techniques. You don't drive like that under normal circumstances, but it's good to have some practice with a trainer in driving school so that when those times come up, you're ready and know what to do.
I'm at an edge personally in my life as I have taken on many projects and don't have much of a buffer built in time-wise for the unplanned to happen. For example, I stuck a week-long holiday in the middle of a busy period, which is fine, except for the fact that it was right before I was pulling a "stretch" a day later by doing my course in Montreal and then coming back and teaching the next day for the whole weekend at the teacher training. So when the plane was 10 hours late in getting home, my buffer got used up a bit and when I pulled another all-nighter 2 days later, well let's just say I'm at my edge. I'm not worried or freaking out about it and I expect I'll get to stop holding this pose tonight when I go to bed.
Then I'll stop holding that pose at the edge until the next weekend when I'm doing my course in Montreal again, getting home at 3 am if the weather's good, and then I'm getting on a plane with my daughter to go to California to visit my grandmother. Being on a plane is holding a pose at the edge for me as well as I've already mentioned!
My yoga practice comes in handy in those instances in life when I know I'm going to do something that's potentially uncomfortable for me. But it's doing those things that allows me to have a great big life where I create what I want and just do it. Those might not be the things other people would want, but they're what I want and it's my yoga practice that trains me so I can be in a big stretch and be present at the same time.