Ultimately, it is used to decrease hardware costs by condensing a failover cluster to a single machine. Thus decreasing costs dramatically while providing the same services. Server roles and features are generally designed to operate in isolation. For example, Windows Server 2019 requires a certificate authority and a domain controller to exist on independent servers with independent instances of windows server. This is because additional roles and features adds areas of potential failure as well as adding visible security risks (placing a certificate authority on a domain controller poses the potential for root access to the root certificate). This directly motivates demand for virtual private servers in order to retain conflicting server roles and features on a single hosting machine. Also, the advent of virtual machine encrypted networks decreases pass-through risks that might have otherwise discouraged VPS usage as a legitimate hosting server.
If you are familiar with hosting control panels, shell commands, and you have basic server administration and troubleshooting skills, then unmanaged VPS is the way to go. Note that while you purchase self­ managed VPS, you should be capable of managing applications, software, services installed on your VPS. Also, you must know installation/un­installations, resource monitoring, server performance tweaking and troubleshooting of any technical issues.
There will be a point in your life where the needs of your website will be too much for a shared hosting server to manage and VPS hosting will eventually become a necessity for you. Meanwhile, you need to take great care to ensure that the VPS which you select is appropriate for your needs and requirements. Hence, you need to start by making a list of your requirements and then comparing various servers before coming to a conclusion on the best possible server for you.
A virtual private server (VPS) is a cost-effective way for a small business to gain more flexibility and efficiency than is offered with shared hosting without the expense associated with running a dedicated server. Most small businesses also don’t need all the power of a dedicated server, so VPS provides a good in-between option when you outgrow your shared hosting. Get the power and flexibility of your own server without the cost and complexity of managing outsourced hardware.
Max Ostryzhko:

Essentially, here’s the criteria I would use to judge things – if your site is made up of primarily static, HTML-based content, then you probably don’t need a VPS package.  However, if you have a large amount of files stored, multiple sites, dynamic content, and the possibility of major traffic from time to time, then you might consider upgrading to a VPS. It’s a powerful package that allows you to do more than you could with a shared hosting plan, but requires less investment than a dedicated server.

You could end up purchasing the most expensive VPS in the world and yet, problems are bound to arise. On such occasions, an excellent customer support is almost an integral requirement. If the issue does not allow your server to operate properly and the customer support does not respond within an appropriate time limit, then you will end up losing customers. Hence, make sure that the customer support of the VPS providers is up to the mark.
You’re paying more, so there SHOULD be a minimum uptime guarantee and better server speed. Look for a host that offers 99.5% at a very minimum, although ideally, I’d rather go with someone who offers 99.9%. Search through some reviews as there are many who have put this to the test. For example, any of WHSR’s many web host reviews include an uptime record as one of our key tests.
Thus, you could use servers from other countries as well without facing any difficulties or additional duties from the governments of either country.

This doesn’t happen with VPS hosting because each mini-server has its own allotment of resources. You can’t use more resources than your allotment, but that also means that no other site can take resources from you. Basically, it is like having a smaller size dedicated server without having to pay the hefty ($100 per month or more) price tag that goes with a dedicated server.
Ask most website owners about hosting and they’ll happily explain what shared, dedicated and cloud hosting is. But when it comes to virtual private servers, lots of them aren’t 100% sure what VPS are or what they’re best suited for. Some don’t even know that there is a VPS hosting option. So, to put everyone clearly in the picture, this article will give you a full introduction to VPS.
Hosting company team members stay up to date on best practices, new technologies, and current threats. They also quickly gain on-the-job experience working with a variety of environments and troubleshooting common issues. That means they know how to optimize your environment for performance and security, and they know how to quickly resolve common issues.