[Synaesthesia]

You can easily copy and paste rectangular selections from PDF's into Pages. I haven't found anything analogous on other OS'es. I used this to compile exam questions for my students.

It's also great for editing PDF's, you can markup, reorder, rotate and delete pages with ease. Yes other software does that but not as intuitively as Preview.

You can compress PDF's by exporting them and selecting a filter.

It's also the fastest and best-rendering PDF viewer I've used.