In the Method of Sections, why is it important to make a cut $($step $2)$ through no more than $3$

members?

Because, with more than $3$ members, we can't be assured that the corseres are coplanar

Because $3$ is an odd number.

Because we have only $3$ equilibrium equations $($sum of forces in $x,$ sum of forces in $y,$ moments$)$ to work with

Because we work in $3$ dimensions $(x,y,z).$