One of the things that many people do when they choose to hire a good web designer is to check their portfolio. That is to say they examine the past projects that they have done to see just how impressive it is. If they find that the list of projects that they have handled is impressive then they choose to hire them for their services. Otherwise they find another designer, one whose portfolio they are really impressed with. Web designers know and understand the demand that customers have to look at what kind of work they have handled in the past. That is why they display their portfolio proudly on their website.
There are some web designing companies that have a very long list of clients. It is impossible to give a list of all the people whose work they have handled. That is when they make a short list of all the names that they would like to go up on their website. In some cases they might have to ask the permission of the clients whether they can display their company names or not. If they give permission then they display the names on the portfolio page. But there are many cases where the web designing companies have the rights to the work that they have done and they can display it at their discretion.
The web designing companies would naturally put up the most prestigious brand names that they have handled and the names of the largest corporations whom they count among their clientele. They understand how finicky and partial clients are towards brand names. It is common for people to get impressed by a web designing company that has handled the work of large corporations. Another factor that they take into account is that customers always like to know if the web designers have handled work in their niche. That is why web designing companies display as diverse a portfolio as they possibly can. This way they let it be known that irrespective of the project, the company would be in a position to handle it.
The portfolio page is a powerful marketing tool and acts as a strong magnet for attracting new clients. Its creation should not be taken lightly. For customers it is a good way of checking if the company has the expertise to handle their work or not and they refer to it before hiring the services of the company.
I buy your point. A portfolio is very crucial to win trust of people. Only after looking at the portfolio and the websites mentioned in it, i can place order for my work. An impressive portfolio can win you good points!