Datacenter or residential proxies
The classes are usually explained by price. Price is only the symptom. What decides the choice is what the receiving side sees.
What the two actually are
Datacenter addresses live in hosting facilities: wide channels, steady latency, the lowest price of any class.
Residential addresses belong to home connections. To a platform such an address looks like an ordinary visitor, and it costs several times more. There is also a middle class, ISP: issued by a provider but hosted in a datacenter.
Where datacenter is more than enough
Catalogue sweeps, search results, indexation checks, price collection, API work. In all of these, speed and stability are what matter.
You can settle this in half an hour: take ten addresses of each class and run the same sample. Usually datacenter wins on time and the failure rates are comparable.
Where it is not enough
Platforms that filter hosting ranges wholesale. There a datacenter address is refused at the door, however many of them you have.
The signature is recognisable: the refusal arrives immediately, identically across the whole pool including fresh addresses, and it does not depend on your rate.
Count what the month costs
Residential is normally billed by traffic. On collection work, where you pull hundreds of thousands of pages, the bill grows fast and is hard to predict.
Datacenter with unmetered traffic gives a flat cost: you pay for addresses and you know the figure in advance.
200,000 pages, average page 120 KB traffic ~24 GB residential billed per gigabyte, bill moves datacenter flat fee per address