There are a lot of different factors that will influence your decision to start pressure washing in some way, shape or form, and dirt that has built up to the point where traditional cleaning methods no longer work will be one of them. Some dirt can be wiped away with little more than a damp or moist cloth, but suffice it to say that if the dirt has a large quantity of lipids in it, you would need to take things up a notch in the pressure department at any given point in time.
A big part of the reason why that is the case has to do with the fact that grease is really resistant to water, so much so that very little moisture is able to pass through its cell walls. Hence, if you want to use a pressure washing machine to clean up a particularly grease stained area, you should consider adding some degreaser into the mix. This is a substance that is widely available in the market, and it can enable you to blow grease right out of the park.
The great thing about degreasers is that they come in readymade spray bottles, and you only need a very thin and fine layer to get the job done. Allowing the degreasing agent to settle on the surface gives it some time to break the dirt down, after which a single spray of high pressure water will remove the dirt once and for all. This method is widely known for improving pressure cleaning results, and its user friendly nature makes it rather popular among newbies in the industry as well as experts with lots of experience.