I usually only recall seeing it where it's the expansion or replacement of a variable with the actual value, when solving equations or similar. It's not great.

I usually only recall seeing it where it's the expansion or replacement of a variable with the actual value, when solving equations or similar. It's not great. I've seen it used in a text talking about programming, with letters: so a(x) was actually multiplication but looked exactly like a function. Ugh!