Though your goal is to to save money, you could end up spending more repairing or replacing your home's siding. Too much pressure can leave dents and divets in the siding, while using the wrong angle for the cleaning can blow the siding off the house. Since pressure washing has enormous power, washing too close to the wall can cause damage to the paint.
While paints can fall off due to excessive water pressure, lead poisoning can occur in homes with lead paint. Professional cleaners know the suitable blow angle and pressure to clean your home's exterior without causing damage.

Use a precise mix of strong chemicals to ensure surfaces look clean and are germ-free. If you're not experienced with the proper ways to handle and mix these chemicals, you shouldn't be handling or mixing them. Improper use of chemicals can lead to skin or eye irritation and internal damage. Plants may absorb chemical substances through splashes or vapors.
Improperly mixed or diluted chemicals can also damage or destroy plants on contact. Handling chemicals without proper protection exposes humans, pets, and plants to burn risk. Experienced pressure cleaners use appropriate PPE to limit chemical exposure.

Many homeowners underestimate the power of the machine washer, and a pressure washer is about 50 times more powerful than a garden hose. High-pressure water can cause lacerations and bruising when it comes in contact with skin, which is dangerous for adults and even more so if children or pets accidentally get in the way. The pressure also makes the hose harder to control, which increases the risk of injuries.
DIY pressure washing saves money but can hurt yourself or your property. Hiring a professional cleaner is the easiest way to escape these problems.