While studying for the 70-433 exam I noticed you can create a covering index in one of the following two ways.

```
CREATE INDEX idx1 ON MyTable (Col1, Col2, Col3)

```

-- OR --

```
CREATE INDEX idx1 ON MyTable (Col1) INCLUDE (Col2, Col3)

```

The INCLUDE clause is new to me. Why would you use it and what guidelines would you suggest in determining whether to create a covering index with or without the INCLUDE clause?