"I want a fast game", "I want a very fast game". This site suggests "rapid", "breakneck", and "dashing" as alternatives for "very fast". "Very fast" is pretty clear very precise compared to those words. Maybe I could speak about "a breakneck pace" instead, but would I have really gained anything other than showing off my vocabulary?
Speaking of very precise, it doesn't even have a suggestion for an alternative to that - though admittedly if I wasn't forcing things I would have phrased that sentence as "more precise than those words".
The idea isn't that "rapid" means "very fast" (I don't think it even necessarily means faster than "fast"). It's that people will use "very fast" when they feel that "fast" lacks the punch the sentence needs, even when they don't actually mean anything different from "fast".
To quote the person I initially responded to
> However, if there is an opportunity to be more exact, one should take it without remorse.
That is what "very fast" commonly does over "fast". It costs next to nothing, and it specifies the meaning slightly more precisely.
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I don't think "rapid" is really a convincing alternative to "very fast" in any case where the "very" is warranted. I liked the "breakneck" suggestion by the site a bit more, but in most contexts I don't think that it's better, just different.
Of course, this all falls completely apart with groups containing a significant number of members with <language> as a second language, where plain speech is required.