I am not 100% sure but I think that relates to amount of power the battery can supply if it is used to start an engine. It is not really relevant when using it as a leisure battery. That said, a leisure battery is designed for deep charge and discharge cycles and not for regular short burst of power as when starting a vehicle.
The Leisure Battery compartments are also designed for certain sized batteries with the terminals in a certain orientation which will limit your choice..
As @WelshGas says, many of the other leisure batteries avilable the dimensions are too high, the compartment where the battery goes is very snug so the replacemnt battery needs to be the exact diemensions of the original.