When you genuinely do not need proxies
Most people asking this question are collecting a few hundred pages a day from a site that has never once tried to stop them. A single address handles that comfortably. What that job needs is a descriptive user-agent so the site owner can see who you are, a delay between requests so you are not the reason their server is slow, and a look at their robots.txt so you know what they have asked for. That combination costs nothing and solves the problem completely.
Buying proxies for a job like that adds cost, adds latency, adds a moving part that can break at three in the morning, and fixes nothing, because nothing was broken.
When proxies are the wrong fix for a real problem
If you are being blocked consistently while sending very little traffic, your address is almost certainly not the cause. Reputation is earned through volume, and at fifty requests a day you have not earned anything. What is far more likely is that your client is identifiable before it sends a single header, through its TLS handshake, or that its headers contradict each other in a way that a browser's never would. Rotating addresses against that problem produces the same block from a hundred different places.
The request fingerprint tool will show you what your client is giving away, and block replay will tell you whether a different address would have made any difference to a specific URL.
The single most expensive mistake
Rotating addresses under a logged-in session. It is the default advice on half the internet and it is wrong for accounts. An account that appears in twelve countries in one minute is a far louder signal than any individual address has ever been, and the outcome is usually a locked account rather than a blocked request. Work that happens inside an account wants one stable, residential-looking origin, held for as long as the session lasts.
Datacenter or residential
Datacenter addresses are several times cheaper per gigabyte and are perfectly good for a large amount of real work: public data, open APIs, monitoring, anything where nobody is filtering by address reputation. They come from hosting ranges, which are easy to identify, which is exactly why they are cheaper.
Residential addresses come from consumer internet providers, so they look like the audience a retail site was built to serve. That is what you are paying the difference for, and it matters on retail, search and social. It is worth starting on the cheaper product and moving up only when you are actually blocked, rather than the other way round.
What no proxy will fix
Enterprise bot management scores the TLS handshake, the header set, the timing and the behavior together. A clean residential address that behaves like a script still scores as a script. Residential addresses raise the odds and are usually necessary for those targets, but they are not sufficient, and any vendor promising otherwise is describing a product that does not exist. Budget engineering time as well as bandwidth, or expect the block rate to improve slightly and then stop.