How to deal with time storage in SQL

-- convert UTC to local time
create FUNCTION [dbo].[udfUtcToLocalTime]
(
    @gmt datetime
)
RETURNS datetime
AS
BEGIN
    DECLARE @dt datetime
    SELECT
        @dt = dateadd(millisecond,datediff(millisecond,getutcdate(), getdate()),@gmt)
    RETURN @dt
END

SELECT dbo.udfUtcToLocalTime(someDateTimeField)
FROM someTable