They are convenient voice command lines. It's faster to speak your timer, ask the weather, play music, or remotely turn off lights than to fiddle with your phone.
Sure... if you have them memorized. Most of the time, the Echo doesn't understand what I'm saying unless I phrase it exactly the same way each time and it pretty much is me learning through trial and error what lines work and what doesn't. Siri, at least on my phone, seems to get natural language better.
