2008 Toyota Yaris Brakes and lines

Hello,
Thanks for the tutorial.

1. Do you require to bleed your lines every time you change your rotors and pads. If so do you check for clear streams of fluid one valve at a time? Or should you have all valves open at the same time?

2. Why do you depress the piston with a C clamp using an old brake pad?

Thanks for your help