American Cedar (which is a member of the Juniper Family) and not cedar at all, will leak sap excessively if not cured properly ... and will impart WAY too much aromatic's into your cigars ...
The "heart wood" contains the oils that possess the qualities to resist and/or repel insects and decay ... that's why it is used in closets, buildings and outdoor furniture, and not very widely used for use in humidors.
American red cedar is inferior to the Spanish cedar in the receptiveness of humidity and unfolds a more intensive smell. Some humidor manufacturers use the American cedar, since it is less expensive and with this wood the danger of encountering resin when working with it is omitted.
Especially when storing the cigars for longer periods of time in the humidor, the cigars will adopt a strong wooden flavor that is generally not desired.