Yes. It's an accessibility thing. It's easier to tell them apart if they're not the same size.

So why wouldn't they just have the denomination embossed in braille?

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.

The Euro has notes of different sizes too.

Mexico has this too. 20 pesos bill, 50 pesos bill and 100 pesos bill are all three different.

Great Britain is the same way. I hate it.

Aesthetically I love how the £50 note looks, in part thanks to its size, but it is really annoying. I guess most people don't often really come in contact with it, but anyone playing in a casino is likely to get them when cashing out, and they stick out of my wallet just a little, but enough to annoy me. And if you're cashing out a decent sum, asking for £20s isn't really an option,too many notes and the wallet won't even fold over.

And I'm pretty sure the euro too.