Here are two situations in which it would be sensible to use a high-pressure cleaning service.
You need to wash a large section of your property exterior quickly
If you need to wash a large section of your property exterior very quickly, then it would be best to have this done by a professional who has high-pressure cleaning equipment. For example, if you're selling your home and have been asked by your real estate agent to prepare it for some viewings at short notice, but your large and long driveway is covered in mud and moss, then this cleaning service could be invaluable.
Whilst it could take you one or two full days to scrub the moss and dirt off this driveway with manual cleaning tools, a cleaner could potentially do both of these things in a couple of hours with their cleaning equipment. This is because the pressurised water this equipment produces can lift multiple layers of dirt off a surface at once and can be used to rapidly and easily push moss off of it, too. As such, in the aforementioned situation, using this service would not only enable you to get your property exterior in tip-top shape in time for the viewings but would also mean you wouldn't need to exhaust yourself in order to achieve this.
You need to wash the upper section of a tall structure that you cannot easily access
If you need to wash the upper section of a tall structure, such as a garage or your two or three-storey house, and this area is one that you cannot access from the ground, then hiring a cleaner who has high-pressure cleaning equipment would be a good idea. The reason for this is that without their help, you would need to climb a ladder and try to scrub the walls by hand (which could take a long time and be difficult, due to you having to keep one hand on a ladder rung to stay balanced whilst also using the other hand to wash the wall).
However, this equipment can produce a very long jet of pressurised water that could reach the upper sections of the wall whilst the equipment itself stays on the ground, without the stream of water losing pressure before it reaches the wall. This, in turn, means that it could remove the dirt from the structure's upper sections quickly, without you having to use any height access equipment that could put you at risk of a fall.