Shared hosting is a good fit for personal blogs, websites for small to medium sized organizations like clubs and churches, and small non-tech business. It it probably not appropriate for a business that relies exclusively on its website for revenue, or for a large organization with a lot of traffic. Also, any type of serious custom develop is usually not a good fit with shared hosting.
Linux VPS hosting is designed for medium size websites with daily page views from 800 to 3000 usually. Some sucking companies over sell hosting accounts on the shared physical server for the competitive price or use obsolete PCs as the servers. There are the major causes of unsatisfaction and customer complaints. Some other small companies don’t have the ability for the technical support required for VPS hosting due to the lack of technicians. Their servers are usually in defect of maintenance and monitoring, and are really risky, insecure and unstable.