pipenv install --ignore-pipfile makes no sense

Question

pipenv install = pipenv lock + pipenv sync.

So If the Pipfile.lock is re-locked, and install from Pipfile.lock, then what is the difference between pipenv install and pipenv install --ignore-pipfile?

I think if we only want to install from Pipfile.lock then we should use pipenv sync instead.

For example:

# Pipfile
[[source]]
url = "https://pypi.org/simple"
verify_ssl = true
name = "pypi"

[packages]
"requests" = "==2.11.0"

[dev-packages]

[requires]
python_version = "3.12"

# Pipfile.lock
{
    "_meta": {
        "hash": {
            "sha256": "7f1be087f2e6adbe8ec64f71bfaaed8b6bb1595f3769488039b14c9d2e555dca"
        },
        "pipfile-spec": 6,
        "requires": {
            "python_version": "3.12"
        },
        "sources": [
            {
                "name": "pypi",
                "url": "https://pypi.org/simple",
                "verify_ssl": true
            }
        ]
    },
    "default": {
        "requests": {
            "hashes": [
                "sha256:09bc1b5f3a56cd8c48d433213a8cba51a67d12936568f73b5f1793fcb0c0979e",
                "sha256:63f1815788157130cee16a933b2ee184038e975f0017306d723ac326b5525b54"
            ],
            "index": "pypi",
            "markers": "python_version >= '3.8'",
            "version": "==2.10.0"
        }
    },
    "develop": {}
}

If I run pipenv install:

$ pipenv install
Pipfile.lock (555dca) out of date: run `pipfile lock` to update to (14165b)...
Running $ pipenv lock then $ pipenv sync.
Locking [packages] dependencies...
Building requirements...
Resolving dependencies...
✔ Success!
Locking [dev-packages] dependencies...
Updated Pipfile.lock (793cf11c853344d4cc8f42ede41e771eb6afaccce2510f7daf1efb578d14165b)!
Installing dependencies from Pipfile.lock (14165b)...
All dependencies are now up-to-date!
Installing dependencies from Pipfile.lock (14165b)...

If I run pipenv install --ignore-pipfile:

$ pipenv install --ignore-pipfile
Pipfile.lock (555dca) out of date: run `pipfile lock` to update to (14165b)...
Running $ pipenv lock then $ pipenv sync.
Locking [packages] dependencies...
Building requirements...
Resolving dependencies...
✔ Success!
Locking [dev-packages] dependencies...
Updated Pipfile.lock (793cf11c853344d4cc8f42ede41e771eb6afaccce2510f7daf1efb578d14165b)!
Installing dependencies from Pipfile.lock (14165b)...
All dependencies are now up-to-date!
Installing dependencies from Pipfile.lock (14165b)...

No difference at all.

If I run pipenv sync:

$ pipenv sync
Installing dependencies from Pipfile.lock (555dca)...
All dependencies are now up-to-date!