Every single time in DGSD DY managed to survive a dangerous situation is a wasted opportunity as far as I am concerned. Can you imagine how awesome DGSD would be if DY died after couple of pages and instead of wasting much of the book on DY we would get to see young XF in action?
When OYF didn't take YG with him right at the beginning of ROCH. Instead of YG complaining all the time and XLN being boring we could have seen crazy OYF and young YG doing all kinds of fun stuff.
When Kunlun 3 Saints He Zudao left Shaolin quickly at the beginning of HSDS. If he had not left so quickly he could have heard Jue Yuan's last recitation of the 9Yang manual as well and the Kunlun sect would become more powerful. (For some reason I always liked the Kunlun sect eventhough the Kunlun disciples in the later parts of HSDS were pretty much all somewhat evil)