A lot of users ask: "Which duplicates can be deleted?"
One can split this question into two:
1) What folders to search?
2) What can be deleted?
So, "What folders to search?"
1) Do not search system folders, such as:
a. The Windows folder - it can have various names, for example, "Windows", "Win", "WinNT", etc.
b. The folder with your programs - it can be named as "Program Files".
c. The folder where files moved to the Recycle Bin are stored - it is called "RECYCLER".
d. The "System Volume Information" folder
All these folders are stored in the root folder of your logical disks (for example, C:\Windows\, D:\RECYCLER\)
What can be deleted?
It depends on which page with results you are:
1) "Complete duplicates" - you can delete any files. You can use "Select automatically".
2) "Similar images" - note that the images are not exact copies, but similar images. So, you should look through all files (the mode "View" - "Images automatically") and decide what should be deleted.
3) "Mp3 files with similar tags" - it is advisable to listen to all unnecessary files using the mode "View" - "Music automatically".
4) "Files with similar names and size" - there are no guarantees that these files are the same. On the other hand, this search method is the fastest one. To check these file you can use the mode "View" - "All files automatically".
5) "Empty files" - you can delete all files using the "Select all" button.
You should take into account two things for better safety:
1) Do not search folders you do not know for duplicates.
2) If there is a risk of deleting a necessary file, select the "Move to Recycle Bin" action
New in version 2.5: Restoring files moved to a separate folder earlier
More info:Find and delete duplicate files