The size of a clone will typically start at around 40MB. This is because a clone is simply creating a VHD mount point that can reference the data image (full copy of the database) plus a local differencing disk. Of course if you make changes to the clone then the size will change. SQL Server thinks clones are full sized database copies, and does not know that a clone is just referencing the data held in the data image. This removes the need to spend hours juggling disk space and allows teams to work in isolation on their own workstations to develop, test and fix code.