eager? in dataframe's checkpoint

[Jean Georges Perrin]

Hey Sparkers,

Trying to understand the Dataframe's checkpoint (not in the context of 
streaming) 
https://spark.apache.org/docs/latest/api/java/org/apache/spark/sql/Dataset.html#checkpoint(boolean)
 
<https://spark.apache.org/docs/latest/api/java/org/apache/spark/sql/Dataset.html#checkpoint(boolean)>

What is the goal of the eager flag?

Thanks!

jg