What does a tonearm contribute to the sound of a turntable?


Curious about how a tonearm affects a turntable sound. I guess it's the piece of the turntable I know the least about and feel the least connection with. how does a really good tonearm affect the sound or not affect the sound? And what about the tonearm does the affecting?
128x128simao
So those of you with the ethos on this: I have the Jelco 750EB coupled with a Hana SL cartridge. Compliance complementary?
@larry5729, you have never heard a great vinyl system.  I have a very nice high end table and arm it is silent and the music just flows.  I am not going to try and change your mind but you are the one missing out.
Hi,
LP's and R2R still rule, and yes getting up from your sofa is a sign of being alive otherwise we end up like humans in Wally.
@simao 

"So those of you with the ethos on this: I have the Jelco 750EB coupled with a Hana SL cartridge. Compliance complementary?"

It is borderline. Light cartridge and medium compliance. 

The Jelco 750 series, however, offer quite a bit of flexibility due to the
fluid damping. I use an even more compliant cartridge (an Accuphase AC2)
on my 750D using the fluid damping and it sounds very good. 

I would definitely use the fluid damping on your Jelco if you are not
already.