ISP proxies are used where a permanent address with a high level of trust is needed: the site sees the address of a home user, while the speed remains at data center level.
Typical tasks
Working with platforms that are picky about data center addresses.
Advertising: checking ads and campaigns in the desired region.
Market research and monitoring competitor prices in a specific country.
Access to regional versions of websites and services.
Long sessions where the address should not change.
Tasks where connection stability and predictable speed are important.
When to consider another format
ISP is more expensive than regular data center proxies — you pay for the trust in the address. If it's not critical for the task, there are cheaper options:
If the site doesn't scrutinize the origin of the address — IPv4 will do: the same speed and permanent address, but cheaper.
If you need many addresses for large tasks at minimal cost — IPv6.
If the address should change on a schedule or by link — Mobile.
If you need wide coverage by countries and cities with constant IP change — Residential.
Detailed comparison — in the article How ISP differs from other proxy formats.