Which of the following statements about scarf joints is true?

Scarf joints are specifically designed to connect shorter lengths of wood to create a longer continuous piece, which is essential in construction when materials are limited. This functionality makes them particularly important for structural elements like plates and sills, where long spans are often required. Each statement regarding scarf joints highlights their importance and functionality in carpentry.

The idea that scarf joints should not be used to support more loads if they fall in a span between posts acknowledges the structural considerations necessary for ensuring safety and integrity in construction. Placing a scarf joint in a location susceptible to significant weight or stress can compromise the joint's stability and should be avoided.

The use of scarf joints is commonly seen in applications requiring solid connections, such as in laying out frames for walls (plates) and in foundations (sills), where creating longer segments is crucial.

Each of these aspects together emphasizes the versatility and critical nature of scarf joints in carpentry, affirming that all statements regarding their application and limitations are indeed correct.