Domestic housekeepers can accomplish many different tasks, but they won't be able to do everything in your house. By the same token, a professional chef can help you with many different kitchen-related jobs, but shouldn't necessarily be expected to clean up.
Knowing what each member of your household staff can and is be able to do is the beginning of creating a better-run home. With a professional domestic staffing firm on your side, it's also possible to find someone with the specific skills for whatever job you aren't currently prepared for. This is also more fair for the employee, since they know they won't be expected to do something that's outside of their skill set if the appropriate people are working there.
For example, the primary duties of a housekeeper are keeping a house clean. However, there are other tasks that the homeowner can do first to prepare. It's unrealistic to expect even a personal cleaner to take care of surfaces and rooms outside of their traditional boundaries, or do any overly strenuous work, like heavy lifting.
That doesn't mean that you could never get someone to assist with these things. In some cases, a professional housekeeper could do some more taxing things for an extra fee. It could be a matter of knowing what they're trained for at the beginning, so there's no miscommunication after the person first begins their work. When it comes to a chef, constant communication is a serious part of the job, and this also includes both client and employee understanding exactly what the expectations for a position are.
Domestic staffing agencies can help employers and their staff begin their relationship on a good note and make sure they know what the job requires.