Running the same spider simultaniously
The only application I see for running at the same time multiple instances of a spider is when each instance will have it's own part of start_urls. But each instance should be run on a different network interface, otherwise you cannot control effectively crawling intensity  for the same domain.
I am using scrapy 0.20 with python 2.7
I want to ask, what is the cons and pros of running the same spider twice in the same time?
Please know that I am using a pipeline in order to write the results to a json file.
Thanks