Yeah Fisher, you just about summed it up there.
There are various ways of acheiving the same thing, backburner that comes with Max can be used to specify which 'job' you want to be rendered by which server. That server will then render that 'job' and save it somewhere.....this leaves the 'host' machine completely free to do other things.
On the other hand, you can also add the 'host' to the server list, so if you have 100 frames to render then each machine will render a different frame until all of them are done. If the machines are identicle then they should render around 50% of the frames each, this ratio will alter if one machine is slower than the other.
Distributed rendering is slightly different in that yes, you can render just one frame but use several servers to do so. The render 'buckets' basically represent the number of cpu's working on the render.
Animations can also be done via distributed rendering, but instead of one machine rendering one frame ALL the servers render the same frame. This does of course mean that the 'host' machine is tied up for the duration.
Thats the general idea behind 'farms'......more processing power when rendering....so it's quicker.
Regards.