Is It true that in SSHD Hard drive we don't need Defragment , Why ?

YES

Yes.

Solid State Drives are not like Regular Hard Drives, data may be saved and accessed in a different process, but there is something called meta data. These meta data when accessed frequently changes in size. 

On a Hard Disk Drive, Fragmenting means indexing the data on the cylinder heads close to the center eliminating it's rotation for faster access.

On an SSD, its surprisingly different though; windows does not index the data like what it does in an HDD, but it checks whether the meta data contains the latest info. Defraging an SSD is something on the data integrity not on the Input/Output or Data Access.

So Yes once a month is default on windows when you frequently save, delete and edit data on your system. It's your preference.

We need Defragmentation to reduce the amount of fragments. We need this process in electro-mechanical HDD to organize content beside each other, so we reduce the need of HDD headers movement, which are relatively slow because they are mechanical components.But in SSHD, they are electronic devices and no need to optimize data fragments since data allocation done with electricity speed and there is no delay if we compare it to Mecha-HDD.