Mice will find a way into unexpected places - including inside the main electrical panel. Chewed wires and debris create a safety hazard.
Home inspectors look in areas that home owners may not think to look or feel comfortable accessing. Significant issues in the main electrical panel such as overloaded panels, defective panels, double-tapped breakers, and rodents (see photo) may be hidden from view. Any of these can be a safety issue and would need to be remedied by a licensed electrician ASAP.
Open electrical panels expose bare live wires which can cause electrical shock and severe injury/death if touched. Electrical panels should only be accessed by individuals trained and qualified to do so.