Not all proxies come from the same kind of infrastructure, and where an IP comes from affects how trustworthy it looks to the website receiving your request.
Datacenter proxies
These come from cloud providers and data centers rather than home internet connections. They're fast, cheap, and easy to get in bulk, which is why free public lists are almost entirely datacenter IPs. The tradeoff is that many sites maintain blocklists of known datacenter IP ranges, so they're more likely to get flagged.
Residential proxies
These route through IP addresses assigned by real internet service providers to real households. Because they look identical to an ordinary visitor, they're much harder for anti-bot systems to distinguish from genuine traffic. They're slower on average and significantly more expensive, usually billed by bandwidth rather than by IP count.
Making the call
If you're checking how a page looks from another country or doing light, occasional scraping, datacenter (including free) proxies are usually enough. If you're scraping a site with serious bot protection at scale, residential proxies are the more realistic option, even though free ones don't really exist.