Welcome to ITKE, JDSAPP! In my opinion, it all depends on your situation. Some of the pros to turning your computer off include electricity costs and the chance to reboot your computer daily (which allows updates). But if you like to leave it on, your computer will be ready immediately for you and it will sometimes perform maintenance (including scanning for viruses and updating software).
To answer your second question, your computer will go into sleep mode when it’s not in use.