How important is passion when building/creating something?

Very. Otherwise, there will be procrastination. I'm not saying that it's bad. But if we are really into some idea, we will never notice time or anything. We will find time.

I think it's motivation for people, and sometimes it's important.

I think it is very important. It constitutes your willingness to put time and effort into your creation.

passion generally serves as the driving force to build/create something. So, passion can affect the process- making/breaking it, quality of the process as well as your own satisfaction ^^