Shortening fry life is the length of time it can be used before it must be discarded. The smoke point is the temperature at which the shortening begins to smoke and break down. If the shortening is smoking the temperature is too high. Fats are usually packed in large blocks, which are hard to handle. The solids don't melt quickly and can easily overheat if the fryer is packed too tightly.
Oils are much easier to handle than fats.
Because they are liquid, oils are easy to pour into a fry vat, do not have the same overheating potential as solids, and are easy to filter. When the temperature is set too high, food overcooks, energy is wasted, and the shortening breaks down quickly. A manufacturer's manual or food product information on the package is the best guide for suggested cooking temperature. It also is important to periodically check the shortening temperature as it will drop significantly, while food is cooking. Some new fryers have a temperature display to allow a visual check of the shortening temperature.