All front-load dumpsters are about 6 feet wide and range in heigh and depth. They are designed to be setup on a weekly scheduled - frequency can range from 1x a week to 6x a week.  There is a specialized truck that loads the dumpster from the front and lift's the container upside down and empties the trash. Once the container is placed back down on the ground, the driver goes to the next closest stop on his route.
A roll-off dumpster is much larger. It does not have lids and it is emptied by a different type of truck. A roll-off container is loaded using a hook or chain that pulls the container onto the back of a truck chassis. The box is then transported to the landfill in order to be emptied. There is no compaction on these trucks. Roll Off dumpsters are most often used for large bulky items (wood pallets, brush, debris, furniture) or for construction projects.