Have you ever wondered what the time difference was between, say, Brisbane and Dubai*?
If you wanted to spend some time studying abroad, or if you need to contact a friend or colleague who is in a different time zone, it can be very useful to be able to quickly check the time in different locations.
That's where a site like Time and Date's World Clock comes in handy. At a quick glance, you can check the times across a reasonably extensive range of capital cities. By clicking on the name of the city, you can also find other details, like: when daylight saving time starts/finishes, the dialling codes for the country/area, the weather... that sort of thing.
There are other sites out there which offer similar services, and I encourage you to have a look around to see if you find one you prefer. Time and Date is simple enough to use, though, and is perfectly adequate for answering those quick, what-time-is-it-in-Adelaide-type questions.
Certainly worth bookmarking.
*(It's approximately six hours, by the way - when it's 11:00am in Brisbane, it's 5:00am in Dubai, give or take daylight savings)