Show HN: A website that makes your text look cool anywhere online using Unicode

Feel like I should be able to explain this, but I can't. What's the downside of using unicode? I note some webpages have UTF-8 in the head. Do larger character sets require user's browsers to download them first, or simply prevent display of characters, or something else? If bandwidth is the problem, how large are the files (i.e how delayed will the site load be). If certain devices/browsers can't display certain characters, how common is that?

In UTF-8, your standard latin characters are encoded just as they are in ASCII (1-byte each), and all UTF-8 characters are 1-4 bytes. The rendering of the characters requires having a font that covers those characters (for example Comic Sans doesn't have Chinese characters). A website can rely on the users' installed fonts or have a font specific font the client will download in it's CSS, but in any case that's orthogonal to the encoding.

https://en.wikipedia.org/wiki/UTF-8#Description