Hi, i am new comer in vue and i have trouble reading the docs

following sentence are copied from the doc

Note that when used as a route component in vue-router, these properties will be ignored because async components are resolved upfront before the route navigation happens. You also need to use vue-router 2.4.0+ if you wish to use the above syntax for route components.

I wonder what it truly means?

if these properties will be ignored, why i use it for route components?

Also, i noticed that relative docs are updated 2 days ago

Note that you must use Vue Router 2.4.0+ if you wish to use the above syntax for route components.

I am very confused.