Hi and welcome to this blog post where I would like to provide you with my experience of using https://laravel.com/docs/master/artisan and https://laravel.com/docs/master/queues within Laravel. Commands and queue jobs help deferring tasks for a later time.
This can also worsen the experience of other users navigating to other pages since the server will be busy both serving web pages and sending emails.
In fact, Laravel requires to setup a "master" command (called the Scheduler), in order to regularily check for commands to run.
Since scheduled tasks obeys to a time, you cannot take the risk of having 4 servers running the same cron job (risky).