Most jib cranes have a simple design. Floor mounted jib cranes are generally built in an L shape. While there are wall mounted jib cranes available, mounting job cranes to the floor allows them to carry great loads.
The portable jib crane was originally designed for the same reason any crane is designed. More importantly, this crane design does not make any damage done to the foundation. It does not require being mounted to the floor and it is extremely useful in cases where the crane needs to be moved from area to area for whatever purpose is required of it.