Whenever you are browsing the web, you make use of a browser. The browser required a means of communicating with the server and identifying itself. This means that the server should know the browser type that is requesting for a web page in order to be able to serve it the most appropriate version. User agents are unique identifiers for browsers that make it possible to retrieve an appropriate web page or version of the website from the internet. They represent unique information about the browser and the operating system on which this browser has been installed. They are useful for keeping the browsers in sync with the web servers that are providing the information and will ensure that your data is accurate.
You only get to be served with information that is relevant to you when you have an appropriate user agent on your browser. For instance, a mobile browser will present a different user agent to the web server as compared to a desktop browser. This means that the information which will get sent down to the browsers will be different as the mobile browser will get a version that is optimized for mobile devices. This will be a version that has a lighter version of the media and a layout that encourages mobile viewing. This is useful for modern internet usage as mobile users do not like spending a lot of time going through the bulk of the information on a website. Instead, they like to go over the website in a few minutes and get to understand what it is all about.
User agents are also used for security purposes. In order for the security certificates to be accepted and a connection to the web server to be encrypted, the user agent must first be sent to the web server. This will make it possible for the server to send its acknowledgement information down to the browser and establish a secure connection. Email applications are particularly dependent on the user agent to ensure that the encryption takes place securely. The client will be required to provide its key and this has to match up with the key that is on the server. In a way, a user agent prevents an impersonation attack on a web server as the client has to be unique and confirm their identity to the web server before any information can be passed.
Using the internet is more organized when there is a way to confirm and verify the identity of the parties that take part in the communication. Whenever a web browser is establishing a connection with the web server, it needs to use the user agent as a way of identifying itself. This way, a secure connection gets to be established and the web server will be able to send down secure copies of its resources. This includes web pages, emails and other useful information that has to be sent to the correct client otherwise it will get intercepted by hackers.