Productivity application clients like a spreadsheet or document editor tend to do best when they can receive commands/updates to the document in the background

Productivity application clients like a spreadsheet or document editor tend to do best when they can receive commands/updates to the document in the background via something like a WebSocket. Otherwise, each time you switched tabs to your spreadsheet, doc, slide show, etc., it would have to poll for changes from the server in some fashion, and wait for a response. This gets pretty frustrating when you're trying to do something like copy from one document to another.