Hydraulic blocks are commonly used by large equipment that use hydraulics. Hydraulic blocks are placed beneath the feet of hydraulic legs that offer support for large equipment. A lot of large equipment used in construction has hydraulic legs that keep equipment steady allowing them to do their job more efficiently.
Concrete construction is an area of construction where this is common. Concrete pump trucks need to be level and secure. If a pump truck is not level it will not be able to pump the concrete as needed. In order to level a pumping truck the pump truck has several hydraulic legs that extend out and lift the truck to the needed height. Since these trucks are on construction sites the ground is commonly muddy and soft. Hydraulic blocks come in many shapes and sizes and a pump truck will have blocks of varying sizes. When dealing with muddy ground the block is very wide in order to spread the pressure of the leg out over a larger area.
It is common to see pump trucks pick up scrap beams and other large wood material from a construction site for their hydraulic blocks. It is a better idea to buy blocks that allow you to specify the size and material of the block.