Question

Why are the components of a vector usually chosen to be in mutually perpendicular directions?

besides the fact that this is easier than other methods

Answer 1

easier to do transformations and computation with basis vectors

Answer 2

actually not all the time, its just easier for people to see the big picture with basis vectors

Answer 3

if u are using unit vectors that are not mutually perpendicular then u have some redundancy when u are performing operations on it, like you will be adding part of the vector that already exists on one of the chosen component vectors only a small part of the other component will result in the new direction u want