The house is made up of many parts that interact with each other, and at some point they are dependent. For the Home Inspector, it is very important to know each of them and how they are related.
Many of the major problems, chronic or minor, are not easily visible or are not in any way, it is there where the inspector tries to looking for symptoms or evidence to find the anomalies that may be affecting the house today or in a near future.
Many times the anomalies of a dwelling cannot be detected at the time of the inspection; consider that an inspector will be at home only a few hours and upon conditions that do not necessarily trigger those eventual problems, but even so, the opinion of the inspector will result in a valuable document for the decision of both the seller or the potential buyer.
We like to say that a Home Inspector is like a general practitioner, who has extensive knowledge but is not a specialist. At the time of diagnostic, the Home Inspector, as well as the general practitioner, will surely recommend the visit of a specialist who will provide a more accurate diagnostic and remediation.
For the client, it will always be more expensive and complicated to coordinate the call to a specialist for each part of the house: plumbers, electricians, roofing installers, etc. Conversely, a Home Inspector with preparation and knowledge can be very helpful.