There are special boundary conditions for mobile machines (excavators, cranes, loaders, etc.). These conditions are due in part to the mobility, and in part to the tasks and environmental conditions. This leads to special requirements in terms of design too for the hydraulic devices used, which justify them being put together in their own group. Having said this, the category does not usually cover the hydraulics used in vehicles (cars, trucks, special vehicles), for which a separate group known as "vehicle hydraulics" has emerged.
We now therefore have both mobile hydraulics and stationary hydraulics.