Question: What are the reasons or security reasons why a URL would be linked this way 

```
http://www.sampledemo.com/redirect?id=17&link=http://www.sampledemo.com/manual.php

```

instead of this way

```
http://www.sampledemo.com/manual.php

```

Thank you

Answer: 
If the URI was properly encoded (it isn't), then the only reasons I can think of are logging the hit and/or displaying a message to the user before they click to continue.
There is no security reason. Usually something like this is used to track, where a visitor comes from. `redirect` will evaluate the `id`-parameter, that usually specifies one concrete (registered) referer and then redirect to the target page.