A VPS runs its own copy of an operating system (OS), and customers may have superuser-level access to that operating system instance, so they can install almost any software that runs on that OS. For many purposes they are functionally equivalent to a dedicated physical server, and being software-defined, are able to be much more easily created and configured. They are priced much lower than an equivalent physical server. However, as they share the underlying physical hardware with other VPSes, performance may be lower, depending on the workload of any other executing virtual machines.[1]
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’ll also Benefit from the Following Features:

Website owners with misconfigured CMS scripts or out of date security versions of code risk MySQL injections particularly that can lead to the theft of an entire database. VPS admin login panels, cPanel logins, FTP connection routes, and email servers running on Apache are all common attack vectors for script bots which are programmed to target common URL structures on domains.

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.
The force driving server virtualization is similar to that which led to the development of time-sharing and multiprogramming in the past. Although the resources are still shared, as under the time-sharing model, virtualization provides a higher level of security, dependent on the type of virtualization used, as the individual virtual servers are mostly isolated from each other and may run their own full-fledged operating system which can be independently rebooted as a virtual instance.
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.
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.