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.
You'd be surprised at how often it happens to singular comments too (not a full shadow ban). Put your username into a site like Reveddit and you'll see which of your comments were deleted without notice by mods or admins. You'd never even know it unless you check with the way you described or using a tool like reveddit.