Pros

Let's start with the pluses of web dating.
1. Easy access. You are short of time or just too lazy to go out to club, bar, cinema after work to meet someone there. But You can do it from your laptop lying on your sofa anytime. The profiles of the users are available 24/7 and your message will be read when the person is online.
2. If You are too shy by nature the dating site really works for you. Writing a message to someone, You don't have guarantee that he will take interest in you and reply. But You can see his eyes, his reaction, thus the first step is much easier. And even if he didn't reply, You have millions reasons for this. It doesn't mean he didn't like you, right? Anyway, You self-esteem will not suffer.
3. The choice of candidates is really big. Just set your parameters and You will have thousands of interesting profiles to look through. You can examine them carefully and reply to each of them or just send same copy-paste messages to all. You will get the answer in any case. The most important thing that You can choose them even without talking to them.
4. You can see beforehand the details You are embarrassed to answer in real. They are concerning sexual preferences, bad habits, dating purposes. Do You ask for sexual needs on your first, or may be second meeting? But people can be really sexually incompatible. Such relationship will not last long. Besides You can find out what kind of relationship a person prefers.
5. You can stop the communication anytime. Virtual relationship is totally under your control, once You realized "it is not for me", You can just delete his profile and ignore him. Reliable dating sites will never give your personal information until You are ready to share it.
6. The number of users is constantly increasing! You'll never have the feeling You know everyone.