The DS Lite's speakers are certainly nothing to be ashamed of. They deliver fairly crisp sound (Elite Beat Agents is a wonderful example) at a decent volume. Still, is this enough in public places? Or are you simply too embarrassed for some games' vibrational happiness to be transmitted to the people around you?
Certainly, headphones can offer a more immersive experience in a game. However, the inconvenience of having to carry around an extra device may outweigh the benefits for some. Do you use headphones, and if you do, are they a quality set? How often do you use them? Let's hear it, people.
And if a tree falls in the woods, it totally makes a sound. That question is ridiculous.