Some people like to put, for example, their current git branch in the prompt. To get that means at least naively, running a git command on every single line the prompt renders on. Git is fast, but it's easy to add a bunch of these and suddenly your prompt takes 100ms to render. Hit enter a few times and you'll immediately notice lag. For that reason, doing this fast does make a real difference.

Of course the fastest thing is to just not stuff your prompt full of detail.

Every single time your prompt appears, your shell is doing something. I've tried using various prompt customising things in the past, but they've almost all been written in shell, and always been palpably slow. To the degree that I've found it irritating and stopped using them.

Starship is the first one that hasn't irritated me, in no small part because it's lightning fast, typically only couple of milliseconds to gather and render the prompt.

This is the first time I've been able to stick with one.

In this case it‘s about the actual startup time of your shell. When launching a new terminal, starship always need to perform its initialization. If it were slow, I wouldn’t use it because waiting seconds before being able to input anything is kind of annoying. That‘s what they’re referring to.

I used to use spaceship prompt before this, and it would often take 5s to open up a new terminal and wait for the prompt to load, starship is always instant (like a prompt should be).

I've tried tools in this space which add hundreds of milliseconds to a shell's start-up time. That's easily noticeable, especially when the system is under heavy load.