A couple of reasons for raw oil.

Boiled oil isn't really boiled oil anymore. It's chemically altered (a sixties thing) with hydrocarbons (I think) to make it "go off". The problem is that unless you add an additional catalyst, like Japan hardener, it goes off extremely slow. This usually leads to the "tacky" condition Ed spoke of. The finish doesn't really soak in, but tends to lay there and coagulate. You want a real mess? Try to clean drywall dust out of a boiled oil finish that hasn't really gone off. Don't go there.

Raw linseed oil, on the other hand, seems to have the ability to migrate into the surface of the wood. By adding turpentine as a vehicle, it soaks in even further. Sawing off a sample of white oak that has been treated with this mixture will show 1/2" or more of penetration. Pretty amazing in my book. Since the oil/turp mix tends to soak in rapidly, the timber is ready to handle much sooner. Unless it's really cold, it should handle fine in a day or two.

The other reason for raw is the "repairability" factor. Boiled oil finishes will not sand well, so it's hard to take out superman footprints that show up a couple days after the raising. Raw oil is very sandable, and actually makes a very suitable base for other finishes (or refinishing) that might be needed say in a bathroom or pool area. Just let in dry, and check for compatabilty.

I have heard some rumors that linseed oil finish will blacken in certain conditions. I have yet to have this happen. We have used it in sunpaces, direct sunlight, bathrooms and kitchens. I suspect this may actually be a mildew condition that does often occur if a frame is paneled in over a fresh slab or foundation.