Many websites today ask you to provide some kind of confirmation when you want to sign up for a service. This includes most things like shopping sites, email accounts, discussion forums, game services, blogs, social media, etc. The main form of verification is simply providing an email address or maybe checking a captcha to verify that you are a real person and not a robot.
Other forms of verification might try to be a little more secure by requiring you to enter more personal information, such as your name, address, or postal code. Another method to determine if you are an authorized user is through phone verification, which is usually an SMS message with a code sent to your phone.
The problem is that not everyone can or wants to reveal their own phone number. Here comes the need for a temporary or fake number to receive an SMS. You can also use a phone number generator with SMS services.
Some important services may use the more secure two-factor authentication where it would be wise to use your real contact number. But for other things that are not that important or only require a one-time verification, it might be better to use a number that is not associated with your own phone.
Fortunately, there are websites that offer a service where you can get text messages sent to a virtual phone number. Using such apps or websites is very useful for one-time verification without compromising your security.