Basically lets your computer know there’s more space on the drive 

 When you clone a 1tb drive to a 2tb drive, you will have a 2tb drive with a 1tb partition (cloned from your original drive) and 1tb of unallocated space left over. You want to resize the partition you cloned to then include the remaining unallocated space in your new drive.  

 Resizing the partition doesn't wipe the data? 

 No, you can add the unallocated space to the existing partition. You can use easeus partition manager for easy mode. Or clonezilla for expert mode.