We've had a number of D&D 5e homebrew questions that present a piece of homebrew (a race, a class, etc) and ask if it is balanced. Some get closed as too broad or primarily opinion-based, others are readily accepted and get answered.
If I needed to ask about whether my homebrew thingy is balanced, how should I do so? What do I need to do to ensure it's well-received and has acceptable answers? What's going on with the closures that I should look to avoid?
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Usually, homebrewing something is about creating a new thing that does some particular stuff that you want, but is inexistent in the original published content, or to solve something you think it is a problem. For example, this question is about rebalancing winged races, which OP sees as problematic/unbalanced. This one is about elemental flavor. State your problem, what you wanted to achieve with that homebrew. This opens up for better answers than "Your homebrew is too strong" or "Your homebrew will never see play".
Then, after presenting your problem, you might present your solution and why you want to solve it that way. This is where you will present us your homebrew stuff. Try to explain your thought process behind each feature, what flavor it had, why did you think it was a good idea. As an example of not doing it, this question got some downvotes and even was closed (probably) because it presents nothing on the thought process behind those features.
I think these two points are the most essential for getting a good answer. We can always give a broad mechanical answer comparing it to published races and the overall balance and synergy, but it might not actually solve the problem.
If you have a specific campaign in mind where you are using that homebrew, tell us about it. Many (and when I say many, I say MANY) features fluctuate between useless and overpowered depending on the campaign. Flying is probably the best example I can think: it's utterly broken in open areas in Tier 1 campaigns, it does nothing inside a cave with a 7.5ft ceiling. Damage resistances are strong if and only if there are enemies that actually use that type of damage against you. Anyway, most features are situational and providing us the situation you're expecting them to show up is incredibly important.
I've seen these questions about homebrew classes and races appearing for a while, and to be honest, they've never sat well with me. I personally think they should all be closed. The reason is twofold: They are examples of "bad subjective" questions, and they won't be helpful to future readers on this site.
There are several issues that lead me to believe questions about homebrew classes are bad subjective. In the overwhelming majority of cases, no one on this site (often not even the asker) has actually played the homebrew class in question, so it's impossible to answer them with direct evidence or experience. While there are homebrew classes that are clearly over- or underpowered, oftentimes what will be balanced for one group will be unbalanced for another due to differences in playstyles and how the groups' campaigns are going, so it's difficult to speak authoritatively about whether a class is balanced. "Balanced" can be a loaded term that means different things to different people. And since the question asks about homebrew, it necessarily takes us well out of the territory of understanding rules as written or rules as intended and asks us to try to tune an entirely new addition to a game system altogether. With all of these issues piled on top of each other for each question about a homebrew class or race, it becomes impossible to write an answer that doesn't, at some level, incorporate one's entirely subjective opinion.
But even if someone asks a question about their homebrew race that avoids these issues - say, by giving a very clear definition for what they consider balanced that can be largely calculated numerically, making the question objective - I still think the questions aren't a good fit for this website. This is because the StackExchange network isn't primarily about helping people with their questions; rather, it's about building a knowledge base that can be searched through by people with some expertise to get common questions addressed quickly. Given that the overwhelming majority of homebrew classes are only played by a small number of people, the only person who's realistically going to benefit from having a question about balancing a specific homebrew class is the question's asker. After that, the question will be noise. By allowing these questions on this site, we are diluting the signal-to-noise ratio on this site.
