What is the difference between transferring a fsmo role and seizing one which one should you not seize why?

Seizing an FSMO can be a destructive process and should only be attempted if the existing server with the FSMO is no longer available.

If the domain controller that is the Schema Master FSMO role holder is temporarily unavailable, DO NOT seize the Schema Master role.

If you are going to seize the Schema Master, you must permanently disconnect the current Schema Master from the network.

If you seize the Schema Master role, the boot drive on the original Schema Master must be completely reformatted and the operating system must be cleanly installed, if you intend to return this computer to the network.

NOTE: The Boot Partition contains the system files (\System32). The System Partition is the partition that contains the startup files, NTDetect.com, NTLDR, Boot.ini, and possibly Ntbootdd.sys.

The Active Directory Installation Wizard (Dcpromo.exe) assigns all 5 FSMO roles to the first domain controller in the forest root domain. The first domain controller in each new child or tree domain is assigned the three domain-wide roles. Domain controllers continue to own FSMO roles until they are reassigned by using one of the following methods: