If you really need the answer immediately to show to a user on a page, background workers (usually) don't help. However, there are a bunch of situations where t

If you really need the answer immediately to show to a user on a page, background workers (usually) don't help. However, there are a bunch of situations where there is no feedback to the user other than "we received your request in good order and will see that it's done". For example, sending a mail can take a while because mailservers have queues and whatnot. If you send a mail after signing up a user for them to verify their email, you don't have to wait until the mail is "really" sent before letting them know that their signup has been processed. You can tell a background worker to send the mail and return to the user much faster. For another example, in a previous job I worked for a big file sharing service. If user wanted their files deleted that caused all sorts of calls to AWS to actually delete the files, which could take a while. However, from the user perspective it was pretty fast because all we had to do was set the file in the database to "delete in progress" state and tell a background worker to delete the files. Then we could show the user that their files were being deleted within a couple dozen milliseconds instead of having to wait for all the AWS calls to complete.