Clone seems to create particles repeatedly around it. The particles are dependant of the clone particles' ctype. The ctype can be added from Console, by using PROP tool or by putting something next to the clone particle itself for the first time after it's creation.
Clone's infinite cloning behaviour has many uses.
Powered Clone (PCLN) is a material that acts like normal clone, but needs to be activated with P-type Silicon. It can be deactivated after activation with N-type Silicon. It is in Powered Materials section. It is element number 74.
Breakable Clone (BCLN) is a material in the Special section. It acts like Clone, but can be broken in the same manner as Goo. It is element number 93.
Powered Breakable Edit
Lastly, in Powered Materials, there is a Powered Breakable Clone (PBCN). Acting like Powered Clone, it acts like Goo, like the Breakable Clone. It is element number 153.