Using Streaming API in Lightning requires disabling In-App Notification and Mobile Push Notifications -- because both of these features use CometD (Streaming API) and you can only have one CometD session going at a time. (Salesforce is working on revising libraries to allow piggy-backing on the same CometD channel, but that's roadmapped for Winter '19).
Streaming API is an elegant alternative to polling, so I really want to use it, BUT... I don't know how much people are using in-app notifications. Is that just for communities? Is it a lot to ask customers to turn off notifications in order to use my app?
My alternative is to use polling, once every 10 seconds, multiplied by the number of users. Does that create an unacceptable burden on the server -- doesn't seem like it, though I'm instinctively averse to polling like this.