Hello Rogers,
You do not have to install SQL Server only using a domain account. However,
in a Domain environment, you should use a domain account for SQL Server.
Using a domain account lets SQL Server services communicate with other SQL
Server installations, access network resources and interact with other
Windows applications.
For a local setup, Local System account is not recommended nor for SQL
Server neither SQL Server Agent.
Actually, Local System account has administrative priviliges and has full
rights on the (only) local computer.

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Ekrem Önsoy
> Is it mandatory to install SQL Server under domain user, I can't install
> under local system account? When I tried to install under local system it
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>
> Plz advice.