Working within the industrial and/or engineering industries, you will be familiar with the term inertia, more specifically the formula with which to calculate inertia.  As such, you will know that the formula used to calculate inertia form a very important part of these industries.  It is not uncommon to utilize servo systems in extremely dynamic applications where positioning accuracy and speed are needed.  However, in order to gain optimal performance in a certain system, the load’s moment of inertia at the rotor end should equate the rotor’s moment of inertia.  Mechanical transmissions and coupling elements such as pulleys and gearbox ratios should be taken into account at all times though.  Being a seasoned engineer, you will know that this is not possible at all times.  You should try your best to keep the load inertia to rotor inertia ratio in the region of about 5:1.  The higher the ration between load inertia and rotor inertia, the worse the dynamic performances of a system will subsequently be.