Another surprising place decibels pop up, pretty far from loudness related things, is in image comparison metrics. Peak signal-to-noise ratio is mean squared error normalized by a certain peak intensity and it is generally expressed in dB, i.e. as 10 log10(normalized mse). https://en.m.wikipedia.org/wiki/Peak_signal-to-noise_ratio

Edit: typo

Decibels make a lot of sense for ratios in any kind of signal processing.

They are not that suited to sound, but sound is generally hard to quantify.