Advantages of an DSLR are:
1. Fast autofocus
2. Auto focus also works in low light
3. Much decreased depth of field for selective sharpness of main subject
4. Wider usable range for shutter speed and especially apertures
5. Low noise even at high sensitivities such as ISO-1600
6. Suitable lenses for almost all conceivable shooting situations available
7. Generally much faster operation, e.g. no pause between shots
8. High sophisticated external flash system easy to use
9. Long battery life
10. Better image quality for large print sizes (even if the P&S has more megapixels)
The disadvantages (bigger, heavier, more expensive, no video mode, …) are obvious, but these are the prize to pay for the option to take a picture exactly the way you want it and, consequently, get the result that you want.