Part B is the synthesis volume. The problems often ask you to synthesize a complex natural product core using 10+ steps. The solution manual doesn't just give the final product; it walks you through the retrosynthesis —disconnecting bonds, identifying synthons, and choosing reagents. This is the closest thing to having a post-doc sit next to you.
Advanced organic isn't just "cold = kinetic, hot = thermodynamic." The problems ask you to calculate the difference in activation energies ($\Delta \Delta G^\ddagger$) required to get a 95:5 product ratio. The solution manual provides the step-by-step use of the Arrhenius equation and Eyring equation, which is easy to mess up on an exam.
Part A focuses heavily on pericyclic reactions (Woodward-Hoffmann rules). The textbook explains the theory, but the solutions manual shows you the exact curved arrows moving around a Hückel or Möbius topology. Without the manual, you might think you understand the concept of a [4+2] cycloaddition, but you won't see why the stereochemistry must invert.
This is where the becomes not just a helper, but a necessity.
So, what are students actually using? They are using the (often out of print) or, more commonly, self-published/institutional answer keys compiled by professors from universities like UC Berkeley, MIT, and ETH Zurich.