Testing Proxies

I want to test proxies this week to see how they work and wanted to clear up some confusion

I have internet through comcast so my external ip is added to this device/server then I have access basically to a pool of addresses on different subnets. I saw that I was limited by the amount of data being used.

What are the main purposes of using a rotating ips \ proxies ?

I am aware of per say i have a pbn, i am looking as many hosting companies as possible. It is just the ip addresses right unlike many different vm type devices. Sorry for asking common sense question.

The main purpose is to direct the traffic your trying to create through specifically IPs/places, hit me I have lots of proxies for cheap