Yes, there is a disadvantage to shopping on time for the holidays. Well, I don't know about other disadvantages, but I encountered one. Ja, and only a few days away from my last post, precisely about why you should shop on time!
Here is the reason: if you did your shopping on time -after checking and double checking with everyone the right gifts and everything-, it is highly inconvenient to find some days later a "formal" letter addressed to Santa from your youngest child, with a surprising 75% of the content completely different from what you already ordered to Santa. Worse, Santa told me all my orders arrived already! Returning items is expensive. Why is the letter 75% different? The TV commercials are the guilty ones! Now my child won't stop talking about the other different things watched on TV.
What did I do? This was an emergency, so I called some of my closest relatives, and divided the new burden among them. They were already asking me about what presents to get. Only one item from the list was left "orphaned", so I called Santa again. He didn't like it a bit, but he said OK at the end.