There are basically two ways to repair wood rot or termite damage. You can either replace the wood or repair/reconstruct. The question one would have is how you would determine which way to go.
Reconstruction takes a lot of patience and skill and a will to restore the damage to original as possible.
Layering bondo is a definite skill set, and working it into wood and restoration is another thing altogether. So to answer the question, it really depends where and what the repair is. In this particular case, we first determined what occurred that made this happen is the first place, then made sure that was corrected or repaired first. Then it was determined that the cost to reconstruct was a lot less expensive then to replace, because in this case there where panels that were formed around the 4X6's . If the reconstruction is done correctly, no one will ever know the difference.
How it was done:
Dig out all damaged wood.
Spray existing wood with wood hardener.
Using either plated or outdoor deck screws, screw into the existing wood to form a place where the bondo will adhere to. Screws should be placed at different depths, some placed just slightly below the surface of where the bondo blends into the wood.
Apply the bondo in steps to start forming the wood back to normal… pushing the bondo into the wood to insure there are no internal air gaps.
Use cardboard to help reframe the wood and use Vaseline on the cardboard to assure that when the bondo starts to dry it won’t stick.
Now for the finish work… sand (refill if needed), re-sand if needed and then using a Dremel tool, grind the lines into the bondo to emulate wood. Prime the bondo and paint.