What is the use of DMatrix?

  machine-learning, python, xgboost

The docs say:

Data Matrix used in XGBoost. DMatrix is an internal data structure
that is used by XGBoost, which is optimized for both memory efficiency
and training speed. You can construct DMatrix from multiple different
sources of data.

I get this bit but what’s the difference/use of DMatrix instead of a Pandas Dataframe?

Source: Python Questions