Just wonder, when insert a value to nvarchar2 column, do we always need to put N' ' there?

My tests show ---

For Oracle 8.1.7(character set is not unicode), I have to put N'' there.

For Oracle 9.2.0 server, it works even if I don't put it there. However, I have unicode characterset on this server, so I don't know if that because it's a 9i server, or because that server uses unicode character set.

Oracle 9.2.0 Globalization guide does mentioned the implicit conversion between different characters (which make me feel we don't have to put N'' in 9i). Can somebody make it sure for me? Thanks!