Anyone who has spent any time on meta will have experienced a user who has been question or answer banned and is looking for help. Often letting them know how to improve is what they need to move forward, improve their existing posts and get unbanned. Usually what I like to do is review each downvoted post individually and give specific advice on each post.
However; deleted questions are a major part of the question ban algorithm and so the post usually goes as follows:
Banned-user: Unfortunately I've been post banned, but I can't work out why.
High rep user: Your profile looks ok, do you have any deleted posts.
Banned-user: No, I don't have any deleted posts.
High rep user: [Awkward trying not to accuse the user of lying sentence in which we say they must] + instructions on how to access deleted posts.
Banned-user: I still can't see any deleted posts.
High rep user: They must be old, only recently posted deleted posts can be seen. We'll have to wait for a mod.
[Several hours pass, hopefully a mod turns up]
Mod: yes, you have deleted posts: link, link, link + advice on how to improve.
A perfect example of which happened just a few minutes ago: https://meta.stackexchange.com/questions/222617/i-am-a-serious-programmer-and-i-may-not-ask-questions-on-stack-overflow
The mod's involvement is hoped for as there is obviously no flag used for this. While a mod usually does stop by there is no guarantee. All this takes longer than necessary and shift too much responsibility onto mods.
Allow very high rep users (10k+ or 20k+) to view deleted posts from the profile, this would cut out the need for mod involvement completely as users could be given links to their posts and if improved high rep users could vote to undelete.
This would allow high rep users to give specific advice on specific posts in addition to the general advice they are already given automatically.
This would be in the same way users access their own deleted questions; through a "deleted questions" link at the bottom of the questions page so deleted posts would not be "in your face". Optionally this link could only be available for post banned users further increasing privacy except when you really need people to see your deleted posts1.
1 Although only showing the link for post banned users might actually inadvertently mark out post banned users which may not be desirable.