Using an off-the-shelf physics engine for unrealistic characters often leads to situations where you have to fight the system just to do things that would otherwise be simple. Here are two quick examples:
Your character is probably best represented as a rectangle, however, rectangles do not slide along the ground smoothly, and rectangles do not remain axis-aligned on an incline, so characters in a rigid body physics engine are frequently represented as a rectangle sitting on top of a circular wheel that acts as the "feet" of the character. The circle is less effected by friction, but it's also not prone to "catching" on edges like rectangles are, and it can maintain even contact on an incline. In ad-hoc physics, you just make the character a rectangle and forget about it, because you aren't bound by the rules of physical reality.
Thinking in terms of force: objects in motion tend to remain in motion. If you apply forces to set something in motion, you'll have to apply forces to curtail that motion. I.e. if you push a character forward to start them moving, you'll also have to apply a braking force to stop them. For the precision of a 2D platformer, working in terms of velocities is much more direct and flexible.
That said, most physics engines will allow you to opt-out of realistic simulation, you just lose the bulk of the purpose of the physics engine by doing that, apart from collision detection.
Ad-hoc 2D physics for a platformer is fairly basic, and is probably likely to provide a "tighter" end result. However, if any objects in your game do require realistic physical simulation, e.g. you want to throw a crate at the player and you want it to bounce and roll along the ground, I wouldn't recommend even trying to do that yourself. Just manage your player physics with your own solution, and other world objects with a "real" physics engine.