IRCTC is a the only online ticket website for booking railway tickets in India. Keeping the data of all the trains and real time book ticket and deducting the sit availability is not a game of small kids. IRCTC is having more than 10 servers which is handling the request from 1 million Indian users who book ticket.
Advantages are without waiting for your turn in queue at ticket window from your home using internet you can book ticket real quick, easy user interface, easy way to find the trains from source to destination(new functionality added of finding availability of seats with the help of flexible day options which help user to plan there journey while book ticket), showing availability in real time and fare for the same, Within fraction of time you could book a ticket get the print out or they have started new initiative of sending ticket information to mobile which is valid while travelling too.
Different option of payment provided new one are Indian Rail Rupay Card like top up card where you recharge your card and book ticket(this help you out in misuse of your credit card or debit card or net banking on internet), emi facility has been started with the help of which if you book ticket which cost you much then you can use the facility, door step courier of tickets availability through irctc. Through one website you can book your lunch dinner / hotel / cab and e shopping which is part of the website. Very cheap budget tours are operated which could be useful at various point. IRCTC as a website has some disadvantage too like during the tatkal ticket the server may get down and we may not able to book our ticket but if we look at advantages in form of user interface, ease of use, different options we could at one point ignored the disadvantage too.