Yeah, one can generate as many rows as they want.
And regarding duplicates, it depends on our data type.
example: if the field is Gender and data type will be gender only where u have only two options(Male/Female). In this case if u generate data for 10 rows, there will be duplicates.
At the same time if the field is Emp no and datatype is integers, u can define the sequence as unique. it will generate only unique emp no's.