I was reading Tobias Achterberg's thesis, and on page 138 he mentions the following presolving technique for linear equations (I'm slightly paraphrasing Example 10.2):
Consider the equation $4x_1+7x_2+3x_3+s=20$ with $s\geq0$, and assume that $s$ does not appear in other constraints. Then, we replace the equation with the inequality $4x_1+7x_2+3x_3\leq20$.
What are the benefits of doing this? Sure, this way we remove a variable from the problem, but won't an equivalent variable just be added back in when we bring the MIP to canonical form in order to apply dual simplex?