Feathered edge scarf joints are the simplest of all the different variations you'll find. This basic joint is used extensively when installing house trim, wood boat planking, and most anywhere lengths of wood need to be joined lengthwise to span a total length. When used in a decorative manner such as this the basic joint will easily do the job.
When used in structural applications the basic joint needs to be strengthened. This is accomplished in a variety of ways depending on what it's going to be used for.
When used in timber framing its common to reinforce the joints with thru bolts and even side plates. Wooden pegs are also just as common.