The purpose of this (Carbon::now()) is to return the current time with a Carbon instance. You can also use the laravel helper now(), so you won't need to import the Carbon class.
And the purpose of Carbon is to make it easy to work with timestamps. For example if you are not working with carbon instances, it will be hard to compare timestamps, extract the day of the timestamp, show how much has passed from the date of the carbon instance in a readable way, etc....
I think the Carbon docs are pretty good in order to see the functionallity and some usage examples: https://carbon.nesbot.com/docs/
Really helpful to display many date formats, ie diff for humans, etc. But all based on php, like laravel is php but Taylor implemented many shortcuts and helpers to speed up many things.