Theory...and i don't know how...

[Sekt]

A good example of momentum is, say you have a nail, and you rested a hammer on top of the nail, and pressed as hard as you could. It wouldn't be possible to press the nail in the wood. Now say you used a one inch by one inch piece of wood, but as long as a hammer, and tried to whack the nail in- still wouldn't be able to do this, because in the equation of momentum, you need mass, and speed. Even though you now have speed, as baton of wood is long, you don't have mass, even though you have plenty of power/force/torque. Same with a machine. Some will try to build a machine, not understanding this principle, then because the machine doesn't have enough momentum, it won't drive a large mag. So they'll try to make up for this lack of momentum by using a bigger motor. But then that has its disadvantages, and the machine design suffers.

Say you now used the business end of a hammer. Now you got mass, and velocity, and can easily drive the nail in. Thing is the power hasn't changed when trying to press the nail in, or whack it in with a baton, or use a hammer.
Its the same with a machine. The more mass, say in the form of a flywheel, the more the machine is able to drive the nail in! Even a very small motor will be able to drive the needle in, if it has the correct mass. Although at some point, the mass will become too much for the motors ability to drive it.
A flywheel is effectively a hammer. Then again some prefer to have more or less momentum depending on what suits their style. Just my two cents... the builders here are experts at this kind of thing.