[Vuejs]-Difference between calling watcher with parentheses vs without

watch is lazy by default, meaning it would only run after an initial change to the source has occurred.

adding immediate: true essentially let’s the callback of the watch to run when the component is initialized. In essence, like the do block of a do while loop in certain languages.

you can find more and the deep and eager watch at the docs
https://vuejs.org/guide/essentials/watchers.html