I seriously don't want to get emailed if I were to have someone post on my wall... I really would like it if I didn't get emailed. Also some users might feel the same way... Reason: There are users who would only be able to see it if they were online, and they would only be allowed to reply back if they were to be on their account... I think there are more benefits, so please make it so users don't get forced to be emailed.
As noted here, I've turned off emails for wall posts.