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Ari Lox --
The top of the item automatically includes the item owner's userlink.
The bottom of single-user items includes an automatic copyright notice with the item owner's userlink and username.
In multi-user items, each person's contributions are marked with their username or userlink.
Since the identification of whom the item belongs to is already there, it's not so much a question of good or bad form as that it's not really necessary. Most people don't do it, but there are no site rules about it, and the community doesn't have the authority to say there are any community rules about it.
If you're not using your real name as your handle or username, and want to make that information public, then there's a reason to include a byline, although that's not the only way you could make the information public.
If you don't want to make that information public, then there's a definite reason not to include a byline.
So it's really up to you whether you want to or not.
Hope that helps.