The only numbers I will ever spell are one and zero, and only when using them as a pronoun, or for emphasis, respectively.
Is there ever a reason to not to use symbols when dealing with numbers? Why would "fourteen whatevers" ever be preferable to "14 whatevers". It's just so much easier to read numbers as symbols, not spelled out.
(Caveat, not including multipliers, like "273 billion").
The real style guide is always your reader. If specific numbers may be searched for or copied, it is kinder to use symbols. If your reader is merely reading a number in conversation, it would usually be better to follow the usual style guide.
The more you know and care for your reader, the better your writing will be.