Studies have shown that during an emergency evacuation, it is critical that all passengers and crew evacuate the aircraft within 90 seconds. Seconds wasted to retrieve luggage can seriously degrade the evacuation process, endangering not only one’s own life, but also that of fellow passengers. For example:

• Retrieving luggage and trying to escape with cumbersome luggage will slow down and hinder the evacuation flow and process.

• The chances of fire and smoke during any emergency landing is high, so slowing the evacuation flow can lead to evacuating passengers becoming incapacitated through smoke inhalation.

• Abandoned luggage can become obstructions or tripping hazards and cause escaping passengers to be knocked over and incapacitated.

• Metal parts of the luggage may also cause damage to the evacuation slide.

More information can be found here.