Originally, shadow banning was a way to deal with bots; you give them a view of the site which looks like their spam is there but nobody else sees it. Obviously this is a great way to silence users as well.
Honestly regardless of the context, shadowbanning or even just your post/comment showing up for you but nobody else is one of the biggest gripes I have about Reddit. If it's not approved, it shouldn't show up. You shouldn't have to literally log in on a different account or incognito mode just to see if your post actually went through.