To come to the point.

Paul Leyland

(though the need to include a decimal point when defining well known lines is ugly)

I know what you mean.  It is so much prettier to write 5889.950Å and 5895.924Å than 588.9950nm  and 589.5924nm. It means you get to use a non-ASCII character.  😉

To be serious now: my work was done with a spectrograph with a resolution in excess of 300,000.  The sodium D lines were separated by about a centimetre at the focal plane. Decimal points were essential, even when using wavenumbers (cm^-1) because the centroids of narrow lines could often be measured to better than 0.01cm^-1.