Efficient way of finding distance between two 3D points

Question

I am writing a code in C++ and want to compute distance between two points. Question 1:

I have two points P(x1, y1, z1) and Q(x2, y2, z2) , where x,

Answer 1

Do you need the actual distance? You could use the distance squared to determine if they are the same, and for many other purposes. (saves on the sqrt operation)