The answer, which might sound slightly apathetic, is "basically never."
Since most people don't like answers like that without explanation:
The only complication that can arise from stuck shedding is the constriction of limbs and digits. The reason there is never really a need to worry about this, is because its a SLOW process. Months would have to go by on a dragon who is growing at a decent pace, and the stuck shed would need to be somewhere it could constrict bloodflow (not the back, belly, head, etc.)
The catch-22 with this all is if a dragon is growing fast, it most likely has proper husbandry and a proper diet. Proper husbandry and proper diet prevents shedding issues, thus preventing "stuck shed."
Dragons aren't like snakes and other lizards who require high humidity or sometimes help with their shedding. It's a common misconception and a common worry by many new dragon owners.
-Brandon