The major advantage of using your own IP address (or addresses) is that you have control of your reputation.
ISPs have a tendency to give “preferential” treatment if the email originating from an IP address is static, that IP has been sending for a long time and that it has a good reputation. If they see multiple senders using the same IP address, they have no choice but to take a closer look at the email being sent as the sender keeps changing.
If you send on a regular basis, abide by best practices, and you have a high level of engagement together with a low number of bounces and complaints – your delivery will always be better on your own IP.
In order to qualify and benefit from being on you own dedicated IP, you need to send a minimum of 30,000 emails per month and keep your complaint rate below 0.25% and your bounce rate below 5%.