Why background processing is needed

Since Ruby 1.8 only supports green threads, if you want to process something longish as part of a web request in Rails, it will delay the response. Of course, if the processing is not critical to returning a response to the client, it’s wiser to push the processing to a background queue and return a response immediately.

There are other incidental benefits to using a background job processing queue like, letting a dedicated server, other than the customer facing app server, handle it, assigning priority to jobs, retry on failure etc.