There is a lot of good info on riving green wood into lumber. I have been doing a good bit of it recently, but it's difficult work. Finding good logs and then manipulating them can be difficult and dangerous. And then you have to deal with drying and shrinking.
I am sure I'm the last to the party on this, but I have recently found it worthwhile and fun to rive dimensional lumber that's already been milled into rough boards.
On this desk project for my son, I am starting with reasonably straight-grained stock. On 8/4 or 4/4 boards, you don't need a giant maul or sledge hammer like Curtis Buchanan wields so deftly. A simple hatchet and deadblow hammer gets the split started easily. On stock like this red oak that splits easily, you don't even need a froe. Once the hatchet gets below the surface it's actually more controlled to lift the piece off the ground and let it drop, holding on to the handle of the hatchet. You can get a very controlled split this way.
Ordinarily I might be tempted to get 4 legs out of this piece, but the hatchet doesn't lie. When riving I usually end up with less yield, but the resulting pieces are fairly strong, and the natural sweeps offer (to me) some great design opportunities.
These pieces are ready to joint or turn and have as little run out as you can hope for.
Those who have worked with riven stock can attest that that it planes nicely by virtue of minimizing the grain run out. This is especially nice on curves and steam-bent pieces, where the plane or spokeshave can approach from either direction with little tear-out.