Let's say the size of a particular page is 150 k, so that the visitor of that page transfers 150k into his/her personal computer. Just imagine if there are thousands of customers visiting that page at once, what would be the result? They will be consuming 150MB of space by a rough idea. This is the amount of bandwidth consumed at a single time. Now consider that if same numbers of visitors come across your website 24 hours a day! This analysis reveals that to sustain huge traffic unlimited bandwidth is much important.
But the question is that, are the cheap web hosting or free web hosting companies offering such unlimited bandwidth? Is it possible for them to give unlimited bandwidth for every customer? The reality is that it takes a huge amount of money to have an unlimited bandwidth. It's not possible for the cheap website hosting companies to deliver limitless band width for each customer. So, how do they manage it?
Most of us are familiar with shared web hosting service, and we also know that in shared hosting multiple websites can be accommodated on a single web server. All the websites residing at that server don't require high bandwidth all the times. Only a few of them consume a large bandwidth due to high traffic. Some of the websites even need a very small amount of band width. So, the bandwidth is distributed depending on the website's needs. The companies that exceed their bandwidth requirements up to a certain level, most of the times oblige for some business web hosting plan like dedicated hosting with dedicated server, hardware and software packages that costs very high.
One must be very careful at the time of cheap web hosting selection, because scammers may advertize the word unlimited in their content to attract the new customers but possibly the truth is hidden in terms and conditions. So, it is batter to consult with some experienced webmaster or web hosting reviews.