Difference between client Export/Import and a system refresh

Hi Experts,

I would like to know the diffrence between client Export/Import and System refresh.

Actually i have done client export from our production system and imported it into our quality system, I have asked our functional consultants whether the production data is now available in Quality. They replied me saying whole data of production system is available in Quality system as off date i have copied the export.

The size of the export was around 8GB, How can this have all the data of Production system which is around 600 GB.

In this way what is the use of System refresh which is done by database level ( changing the cntrl file etc... ), As i am getting all the data by doing Client Export/Import.

Thanks & Regards,

Injamuri