BUG: GroupBy Aggregation Behavior
- I have asked my usage related question on [StackOverflow](https://stackoverflow.com/questions/65955108/pandas-groupby-aggregation-behavior).

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#### Question About GroupBy Aggregation Behavior

I observed a behavior of the Pandas GroupBy method `agg()` which I cannot explain based on the [docs](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.groupby.DataFrameGroupBy.aggregate.html).

I want to perform a custom aggregation on a grouped `DataFrame`. Let's take this code snippet:

```python
def aggregate_point(x):
 print(x)
 exit()

data = data.groupby(
 pd.Grouper(level='time', freq='1H')).agg(aggregate_point)
```

This prints a `Series` for each group.

However, when I pass any additional parameter to `aggregate_point`, the full `DataFrame` is being printed:

```python
def aggregate_point(x, score):
 print(x)
 exit()

data = data.groupby(
 pd.Grouper(level='time', freq='1H')).agg(aggregate_point, score=True)
```

Why does the `score` parameter influence the value of `x` (`DataFrame` vs. `Series`)?