Logstash restore option (ouput-s3)

I use logstash-ouput-s3

There is restore option.

Document said
"IMPORTANT: if you use multiple instance of s3, you should specify on one of them the “restore=> true” and on the others “restore => false”. This is hack for not destroy the new files after restoring the initial files. If you do not specify “restore => true” when logstash crashes or is restarted, the files are not sent into the bucket, for example if you have single Instance."

I can not understand what does it mean. could you give me a more infomation?