By far one of the most annoying aspects of Google Now and Assistant is that you have to speak "OK Google," before every command. Even though Now and Assistant can continue conversations based on context (for example, you can follow up "Who is the president?" with "How old is he?"), you still have to say "OK Google" before asking anything.
Google Assistant on Android TV, which is coming to all set-top boxes and televisions running Android TV 6.0 Marshmallow or higher, will support continuous conversation mode. This means that Assistant will keep listening for a short period after responding to a question, in case you want to continue the conversation.
The above video shows the feature in action on the second-generation NVIDIA Shield. In the demo, "OK Google" was only spoken once while the conversation continued to progress through search queries and opening Netflix. I would very much like to see this come to Assistant on the Google Home and Pixel in the near future, but we'll have to wait and see.