Here are a few reasons I found on eHow for having a presence on the web:
A website allows people to instantly access your information at any time of the day. Some folks do their best Web surfing at night and will not wait to contact you during regular daytime hours. Your site allows visitors to immediately find out who you are and what you do.
Websites are also an ideal method for conveniently reaching your audience. When you have new content, such as products or images, there is no need to notify people about it because they can just go to your site and view all the new information that you have published.
Showcasing your work on a website is a valuable tool that fits a variety of industries. For example, if you are a real estate agent, you may have pictures of your available properties on your pages. If you are an artist, you can have a digital portfolio of all of your pieces. By making these images obtainable in this way, people will not need to wait for you to scan your pictures or mail them out. Your body of work will be immediately accessible by simply having a website address.
Credibility is essential for establishing yourself and a website supports this goal. For instance, you can post links to the reputable organizations that you belong to, list the awards that you have won or display customer testimonials. These credentials are important to people, especially if you are a business.
Websites also lend credibility to your purpose. Your Web address and custom email show that you have spent the time developing your goals and objectives.
Your website allows you to promote yourself throughout the Web. You can run ads 24 hours a day, seven days a week and include any images and text that you want. Internet advertising is also significantly lower in cost than traditional marketing methods, such as newspaper ads or direct mail. These tactics are effective on their own and even more so when used in conjunction with other marketing efforts. More importantly, you can now reach people in all parts of the world.
Networking is important for all kinds of aspirations. With a website, you can build a forum and connect with those who share your interests and benefit from the information you provide. You can find others in the same field and create relationships in order to share tips and ideas or solve problems. Furthermore, you can cross-link with other related organizations so that visitors have multiple avenues of finding you on the Web.
To the above list can also easily be added, affordability. For less than $100/year you can have your own domain name (mycoolsite.com), and with a few button clicks install a dynamic blog like WordPress, content management system like Joomla, or web store like Zen Cart or Magneto. For a few dollars more you can even have a professional (like me) develop the site for you.
Having a properly set-up page on a Social Media site like Facebook or Google+ is also an affordable way to interact with your clients, potential customers and constituents of all sorts. The primary reason NOT to have a social media site as your only presence on the web is that these platforms can be rather fly-by-night, whereas your own domain name is yours for as long as the internet lasts, and the sooner you snatch up your desired domain name the sooner it’s securely under your stewardship.