This implies actually knowing Braille. Even in very developed countries, not all blind or visually deficient people know Braille. Arguably, they should be pushed toward Braille rather than left in a "comfort" zone.

There are many ways for Braille to fail, particularly if embossed on a regularly-used banknote, and not everybody can use it. Differently-sized notes are much harder to break, and are potentially useful for everyone. Make the notes differently-coloured as well, and they're straightforwardly distinguished by most people, regardless of disability (or lack thereof), in a variety of situations.

(I would imagine Braille costs a fair bit to print, but banknotes are somewhat expensive to make - compared to most pieces of printed paper, I mean - so perhaps that wouldn't be an issue.)

Because when you are eighty years old and you become progressively blind, it's difficult to learn a completely new 'tactile' language.