It would be convenient to allow message types to exist without alwaysI solidly concur. For all notice types.
I just had to delete the Welcome Message of my PTA group (it only had one Welcome Message) to prevent hundreds of Direct Add newbies from getting both a Direct Add Message and a Welcome Message.
The two would have been redundant because I had put welcoming information (appropriate to the direct add case) in the customization area of the Direct Add Message. I only have a Welcome Message in case someone joins of their own accord.