The fact that you have to parse them that finely for them to be accurate means they are not very useful in general.
When I say 'atheist' and 'atheism', generally I do mean them that accurately and often understand it that way when anybody else uses them terms, but I do at times find people have misconceptions. If I'm going make a generalisation I try to make use of modifiers - or make clear what 'kind' of the atheist I am talking about. I might say, "a gnostic atheist" or "humanists" or "an atheist who believes..." and so on. But of course, we're not perfect in our usage in words and I will make a generalisation just using the word 'atheist' without the extra clarity, if it's unclear then I will correct myself. I guess as you say, semantics.
If I talk about myself as an atheist, I might use my full title, agnostic atheist Buddhist. Unfortunately, because sometimes people don't understand what that actually means I have to explain it. A friend actually said, "how can you be all 3?" Because their understanding was that atheists are non-religious, Buddhism is a religion and an agnostic is the middle ground between 'theist' and 'atheist', therefore all 3 words are incompatible. It is possible to be a religious atheist, as religion doesn't require a god, Buddhism is a grey area, it is at times argued to be a religion due to its supernatural aspects, however, belief in those supernatural aspects is not a pre-requisite for being a Buddhist and because of it's non-dogmatic nature it is also considered a school of philosophy and 'agnostic' can be a modifier for either 'atheist' or 'theist'.  In fact, if I were to say, "I'm agnostic" (so you believe there might be a god), the implied meaning could be different to what's accurate, if I were to say, "I'm an atheist" (so you don't like religion?), the implied meaning could be inaccurate and if i were to say, "I'm a Buddhist" the implied meaning could be inaccurate, (oh, so you're religious?). Regardless of what I say, I'd have to explain myself if I didn't want the person to get the wrong idea.
I did tell a street preacher that I was a Buddhist though (wearing my pentagram t-shirt) and it threw him off balance a bit, but the outcome was the same, I'm going to hell if I don't accept Jesus Christ.
Yes, at times for me to use those 3 words together I have to explain it. But even I loosened my use of 'atheism' I'd still have to offer some explanations as to what I mean, because many still believe atheism = science, evolution, big bang theory, natural selection, humanism and so on, which is inaccurate. Particularly as there are theists who support the theories of science. So, if I have to make the extra effort to educate, then I will - there's a lot of misconceptions out there and if I need to explain myself, I will. I even go as far as correcting people on the capitalisation of the 'a' in atheism. It's a noun that describes a quality about us, not a name. However, I am not a grammar Nazi, so I don't go around quoting people and saying, "your grammar is all wrong", I pick at it when it's relevant and useful (or when a grammar Nazi makes a grammatical error).
But for normal modes of conversation, we hope that we all understand what we mean. If I say, "babies are atheists", I suspect you'll understand that I mean it in the literal context, they've not come to conscious decision about their position on god, but simply lack belief. Yes, I may have to clarify it to somebody else.