General Information
these type of questions usually involves age related questions, place related questions, definitions, time related questions, picture related information, weather related information etc. Certain conversion factors related information and mathematical expression related questions also can be through Google Now.
Device Control
These types of questions usually evolves opening of certain applications, taking pictures with in built camera, recording video etc. It is also possible to turn or turn of Wifi and Bluetooth on request.
Productivity
Sometimes setting an alarm or reminder takes a lot of keystrokes which can be done with Google Now. Setting Timers and starting stop watch etc also can be done through Google Voice Command. Some of the Gmail information also can be used through Google Now using voice command. Creating a note about something also is easier with Google Now.
Communication
Often we want to check the last email or email sent by someone. Or we want to know who called us last or on a specific day. For these type of questions also Google Now can be utilized. texting a particular person or calling someone or sending an email to someone will be much easier with Google Now.