will gig nic in server increase thruput on switch?

i thought i read somewhere that when you go to a switched infrastructure that putting a gig card in the file server will increase performance on the network. I think the logic was that with all the computers talking at 100 on their own segment, the server can be a bottleneck. However, i’m wondering if that is technically accurate. Do i understand correctly that even with a switch, only one node is communicating with a server at one time? If so, wouldn’t the ‘rate determining step’ be the workstation?