Generally plastic sheeting is used to contain affected areas during the remediation process in order to keep the contamination from spreading throughout the structure.
The damage in this picture was caused by an ongoing roof leak which caused the drywall and insulation to be removed. In this case the underlying structure needed to be dried as well as cleaned. Containment was installed to serve two purposes, to keep spores from circulating throughout the rest of the structure and also to keep the drying chamber contained to a small area.
Containment was set up to keep the contamination from spreading to other work areas while remediation was in progress.
If you have a mold problem call SERVPRO of Springfield at 217-528-7775