: Hard woods and soft woods will sand at very different rates.

: It is not uncommon to have an irregular surface if hardwoods and
: softwoods are intermingled. As the sander goes over the surface the
: same speed and pressure will remove different amounts of wood with
: high spots on the hardwood and low spots on the softwood.

Not to start another battle, but this is one situation where a sharp plane can do good things. Otherwise you will have the best result sanding different density woods if you change the sand paper early and often so you are always using the sharpest stuff possible. But if you can get a similar result using all softwoods you will probably be enjoying life a little more.