Android: DDMS Perspective vs Debugging Perspective

I noticed that there are two debugging perspectives in Eclipse that are set for Android development.

Why two?

What does DDMS perspective do that Debug perspective does not?

To clarify, I’m only interested in the diff comparison table, not the complete list of DDMS functions.

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I’m also curious to know why the people who developed DDMS didn’t add it to the Debug perspective, but chose to implement it as an independent perspective.