do you know when you go to a web site and you either post a msg in a forum or try to download something... then you get the screen saying "you will be taken to where you came from shortly" or "you will be redirected to blabla soon" or "your download will start in 15 sec".... but there's a link right below that saying "if you cannot wait click here to go -there- right away"

my questions are:

1. what is going on during the time you are being "redirected"?
2. why is it neccesary to do that?
3. if it's neccesary why put a link below to go there right away?

basically i cannot concieve the reason why would this be neccesary ... can someone elaborate