I never understood why nF is less frequently used than uF or pF. To me, the logical thing is to express the capacity in units that are between 1 and 1000, like it's done with resistors and inductors.
I, too, had wondered; this seems particularly common in the US. My best theory is that in rough handwriting, n and u/μ can look pretty similar, and everyone sort of agreed to only use u to reduce ambiguity.
Another way to reduce ambiguity is to omit the suffix (unless it's p for picofarads) and let it be deduced from the numbers and symbols.
47 -> 47nF (if next to plain double bar symbol with no polarity markings)
47 -> 47μF (if next to polarized cap symbol)
0.47 -> 0.47μF
47p -> 47pF
10np -> np -> nonpolar -> electrolytic -> 10μF
I heard this, and have witnessed it. One of my first jobs included board rework. There were several times when I had to go ask if they wrote a uF or an nF. The response was always "obviously a uF", because nobody uses nF!
Nobody uses nF in, say, digital, where the only caps are power supply filter caps and bypass/decoupling caps next to ICs.
It's not customary to call a 0.1μF bypass cap 100 nF.
If someone wrote in 100 nF for a decoupling cap, I would tend suspect they are trying to discourage a substitution like 82nF or 150nF and want to find out why.
Whereas if it is 0.1μF, I know we can stick in a 0.2μF, if that's what we have on hand, and everything will be fine.
