Why we add a constant value column in our DataFrame sometimes? Currently I'm learning data science and I'm in the beginners stage. I have seen many times we add a "constant" column in our data frame with all row cells of that column having value 1.

I need to know why we do so. And also what will happen if we don't use it.

Thank you.
In linear regression you need that column to have lines which are not constrained to pass through origin. Think of linear model $y = b_1 x_1 + b_2 x_2 + ...$. Iff all $x_i$ are 0, y must be 0, you need an additional parameter to pass that constraint.