Personal opinion, and also dependent on the particular question/answer:
It is not justified to delete a question instead of accepting an answer (this is only possible if there is only one answer with no up-vote), or after receiving a comment (but no answers) that solves the problem. I have seen this happening a few time and might be due to the user being embarrassed about having to ask at all (they shouldn't be).
It is justified to delete a question when you suddenly realize it's off-topic. If you are prevented from doing this (there are a few answers or answers with up-votes), then flag for the attention of a moderator (who will either migrate or close/delete the question, or not).
It is justified to delete your own answer if it's plainly wrong and can not be salvaged. I think this is better than editing it, adding a piece of text saying "this is all wrong".
It is justified to delete your own answer if someone else has a more general, portable and more beautiful solution to the same problem. Personally, I would probably leave my answer in there if it's actually correct (though I have deleted these kinds of answers myself too).
An answer is not just about solving one particular problem. It may give hints to how to go about solving other (possibly unrelated) issues. An inefficient answer may still use a particular quirk of some tool, grammar, or syntax that a reader might not know from before (but now learns), and that the "better" answer doesn't use.
Regarding down-votes: Don't care about them too much. It may sting a bit, but everyone gets down-voted, both on questions and answers. If you write an answer that gathers a few down votes without any explanation, just look at the answer and see if there might be room for a bit of explanatory text. A proper explanation to go with the plain solution may prompt someone to comment, at which point you may realize what the down-vote was about (and whether to retire the answer or to modify it).
If you want input from others on particular answers, ask in the chat or here on Meta.
On-topic questions with proper explanation and context rarely gets down-voted. Again, ask in the chat or here if you need input about improving a down-voted question. People will help depending on their availability and expertise.
I have said nothing about being blocked for deleting too many answers/questions because I did not know that this was a thing.
Related, about deletion: How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion?