In handwritten notes I've done it many times. Mathematicians seem to create them.
On computers I haven't had the opportunity. When adopting new technology people commonly don't imagine the applications - even expert technologists, even those who developed the technology, often don't know.
> Would the added expressive power make up for the inconvenience of having to explain the meaning of the novel symbols?
It's a good question, but I could see definitions working efficiently in many situations. If the symbol is shorthand, it's easy to say 'the population of Hacker News P(H) ...', and it works well in mathematics, 'let Q be _____'. (These are imperfect examples because I can't create new symbols.)
On computers I haven't had the opportunity. When adopting new technology people commonly don't imagine the applications - even expert technologists, even those who developed the technology, often don't know.
> Would the added expressive power make up for the inconvenience of having to explain the meaning of the novel symbols?
It's a good question, but I could see definitions working efficiently in many situations. If the symbol is shorthand, it's easy to say 'the population of Hacker News P(H) ...', and it works well in mathematics, 'let Q be _____'. (These are imperfect examples because I can't create new symbols.)