better safe then sorry.
There's a term called "Situational Awareness". That means you MUST be aware of your surroundings and what is going on around you at ALL times. Doesn't matter if you plan on changing lanes or not, making a turn or not. Check your mirrors, turn your head - it does swivel. When a car enters your blind spot, being aware of your surroundings at all times you'll probably see that car just before it enters your blind spot. Now you know the car is there even if you can't see it.
No, you have a quick look behind too, by turning your head.
yes you should , drive smart, drive safe....