Exhaust Resonator
 

On my 73 450sl there is an exhaust resonator, what is its purpose? Is it needed, what would happen if it was removed?

Just as the name implies, it reduces/eliminates resonance (droning) at speed.
You may be able to live without it, but it was originally installed for that reason. ;)

After doing some major digging on other sites, my understsnding is as follows.

It is nothing but a noise supressor.
It can be removed, using straight pipes to the muffler or a Y pipe.
When removed it should unleash a few extra HP.
When removed it will cause the sound of your car to have more roar or throaty sound.
When removed the reduction of back pressure(even though slightly) might cause the car to run ricker.
When removed you should experence an increass in gas mileage.

This does look like something I might want to try. Cheers.

Go for it!
You must have gathered that information at www.fairytales.com.