Shared private proxies are, as the name suggests, private proxies that are shared between multiple users. This is typically a good choice if you need to browse the web anonymously but don’t have the budget to buy a dedicated private proxy which is more expensive. Since the cost is shared between the individuals who are using the proxies along with you, the amount you need to pay would go down in accordance to the number of people who are sharing the proxies with you.
A few things to note about shared private proxies is that your machine will be more prone to risks of infection via viruses compared to dedicated private proxies which typically come with more protection. Shared proxies come with some level of protection too, but it hardly ever compares to the more expensive alternative.
Depending on the number of proxies you got, the connection will also likely be slower compared to exclusive private proxies. So if you want faster speeds, you will probably have to pay for more proxies which then increases the cost. As such, shared private proxies suit those whose needs are not very demanding.