Performance is never a bad thing, even if I don't always need my terminal emulator to be able to handle large amounts of text, there is nothing wrong with having a light weight high performance (eventually cross platform, hopefully) modern terminal emulator. I read a while back that implementing the same in iterm2 (a popular macOS only terminal emulator) is challenging due to past design decisions [0]. Certainly in a time where hyper terminal[1] (based on electron) exists, I see no downside to having the option of Alacritty.
[0] https://news.ycombinator.com/item?id=17635869 [1] https://hyper.is/