Shipping containers are used not only for transporting goods but also for various other applications like housing projects and for storing goods on-site. One important aspect that has to be taken care of is ventilation - no matter what the container is used for.
Cargo owners prefer airtight containers. They want to prevent air, moisture and insects from entering the container while goods are being transported. When containers are used for other applications like housing projects and for storage at sites, being airtight might actually create problems and this must be resolved through ventilation which is a task performed by experts.