Upon interviewing an individual or company, ask about their methods and techniques. The response should be along these lines.
Regarding wooden fences: There are circumstances that require a wooden fence be soft-washed, and other times when pressure washing is more appropriate. It really depends on the desired result. For example, if one is simply wanting to remove earth, algae, or mold, then soft-washing and a moderate rinse would probably be most appropriate. But if one is preparing a wooden fence for a fresh coat of paint or stain, then pressure-washing is probably the way to go.
Regarding vinyl fences: Because the construction material is sensitive to cracking under pressure, a soft-wash technique followed by a moderate rinse should always be utilized. What a soft-wash will include is a chemical application to safely reduce the bond between the surface of the vinyl and whatever organic matter you’re trying to remove.