It is particularly important to know preparatory variations for challenging asanas. I want to repeat difficult asanas and hold them for longer. On days when nothing seems to work, I practise simpler variations. But there are also days when you want to push the limits. These are the days for the variations that go a little further.
Since my back injury, I've learned one thing: the exercises have to adapt to me and not the other way around. Every series is an offer. You have to train wisely.