Sources:

Software Testing course at ITMO university by Kochubeev Nikolay Sergeevich
https://docs.pytest.org/en/stable/explanation/fixtures.html

Fixtures

Fixture is a defined and reliable context for the tests.

It is useful because of:

The reuse of the arrangement code.
A single initial state for a group of tests.
Simplification and reduction of tests.

Best practices

The fixtures should be minimal — just what is needed for the tests.
Use SetUp/Teardown to clear resources.
In Python and Go, it is convenient to use yield/defer to free up resources.