Portable Generators are used for smaller and less permanent applications, like homes or in building sites. These units are movable can be placed where ever they are required. These portable generators tend to be petrol-fueled.
The main advantage of portable generators is obviously that they can be easily moved to where they are needed. This kind of generator isn't normally used for backup power, but it could be used this way. Simply by storing it on-site, it could be connected to key systems if there is a power cut.
Alternatively, a portable generator could be used to power equipment on a building site. The small size allows the petrol generator to be located where it is needed and moved when necessary.