cc cleaner question

CCleaner for Windows
1

ok i have a dell inspiron running windows vista home premium 64x i am new to this but in the cc cleaner it has wipe free space or entire drive if you select entire drive it says all data will be erased what kind of data

2

ok i have a dell inspiron running windows vista home premium 64x i am new to this but in the cc cleaner it has wipe free space or entire drive if you select entire drive it says all data will be erased what kind of data

Some info here, and here.