By reading https://www.pantsbuild.org/docs/targets I don’t really get in what cases I need a

BUILD

file. Also, after running

pants tailor ::

and

cat **/BUILD

I get something along the lines of:

...

python_sources()
python_sources()
python_sources()
...
python_sources()

python_test_utils(
    name="test_utils",
)

python_tests(
    name="tests",
)
python_tests(
    name="tests",
)
...
python_tests(
    name="tests",
)
python_tests(
    name="tests",
)
python_tests(
    name="tests",
)
python_tests(
    name="tests",
)
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
python_sources()
...