I ask you a simple question: is it D letter or D-letter? X axis or X-axis? (just some random words)
I haven't found an answer to that anywhere. Even Google couldn't give me a clear answer. Is there a difference between British English and American English or is it just an insignificant thing?
Insignificant I think. Hyphens are just used to clear things up usually or to attach something so it's more obvious. X axis is read easily and someone should be able to figure it out, X-axis looks the same but slight difference in that its paired and there's no mistake whether axis is connect to it or its starting to say something else beginning with the word axis.
Generally I just think of the hyphen as another letter and you need to just know how to spell words that contain them. Aside from compound modifiers, that is. Then there are also times when using the hyphen is just natural, especially when making up words. I'd give an example since I use it quite often, but I'm too lazy to dig up any recent writings.
Language is used for communication. The difference between British English and American is as insignificant as the difference between British fashion and American fashion
I personally use what's convenient for the intended audience. I bother with things as hyphens and semicolons in more formal writing (they type with 1.5 spacing), but otherwise, it's better to get rid of it as it's ugly. Or not. Depends on your taste.
Disclaimer: Any sarcasm in my posts will not be mentioned as that would ruin the purpose. It is assumed that the reader is intelligent enough to tell the difference between what is sarcasm and what is not.
When writing I tend to use hyphens quite a bit, especially in things like "hilariously-named Person", "wrongly-awarded penalty" and words like "mid-table", "pre-season", "play-off". I suspect it might have something to do with British and American conventions, but I was never taught to use hyphens, and there's no real 'right' way. Or there isn't any more at least.
As an aside, I would always say X-axis, but would have nothing against X axis either.