IPv4 proxies are used where a permanent address, high speed, and predictable cost are needed.
Typical tasks
Public data collection: website parsing, competitor price monitoring, filling databases for analytics.
SEO: checking positions and results from different countries, tracking changes in search.
Ad verification: how an ad looks to a user from the desired region.
Automation and multi-threaded work, where channel speed is important.
Testing websites and applications from different IP addresses.
Any services where the same address is needed for a long period.
When to consider another format
An IPv4 address belongs to a data center, and websites can see this. For most tasks, this does not interfere, but there are cases where another format is better suited:
If the resource strictly checks the origin of the address and expects home internet — ISP or Residential will be suitable.
If many addresses are needed for mass tasks at the lowest price — IPv6.
If the address should change on a schedule or by link — Mobile or Residential.
Detailed comparison — in the article How IPv4 differs from other proxy formats.