Usually you try to load a web page in the quickest possible time. Usually…
The loading screens you see primarily on travel websites are artificial. Finding the cheapest flights, the best hotels, and whatever else you may be looking for takes less than a second. In fact, a lot of hard work goes into making all that information very easily accessible for the web app.
The loading screen exists because when the information is returned to the user as quickly as possible, he or she will often perceive it to be less valuable. It’s as if the server didn’t put much effort into really finding a great deal. No customer ever actually articulates that; but surveys, customer testing sessions, and most importantly conversion rates support the notion that when a seven or eight second loading screen tells the user that the numbers are being crunched just for this one query, the result is perceived to be more valuable.