11gr2 PARALLEL_DEGREE_POLICY is AUTO

I am having trouble understanding what this parameter means. Just by its fancy title it says that

if PARALLEL_DEGREE_POLICY is AUTO then instead of writing

SELECT /* parallel (4 big_table) */
col1,col2 .........
from big_table

i can simply do this
SELECT
col1,col2 .........
from big_table

and oracle depending upon the size would decide what parallelism to use is my understanding correct       

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