Why Inter Rail?

"Interrailing" is less popular in these days of discount airlines and various affordable air passes, but it remains a uniquely flexible way to travel — you can literally arrive at a city, decide you don't like the look of it, and zoom off on the next train out. This makes it a great way to get a feel for a large region, especially when heading out into the countryside. Do not, however, fall into the trap of traveling so continuously that all you see is a blur of railway stations; it's always best to spend a minimum of three nights per destination so you can settle down a bit.

source: http://wikitravel.org/en/Inter_Rail#Why_Inter_Rail.3F