Bottlenecks on a network(best practices?)

Hello everyone,

I wanted to just clarify regarding where bottlenecks occur on a network. Hypothetically, I have a router with a gig port, where all of the routing tables sit and I have my backbone switch connected up to that port(with all of the other switches patched to that back-bone switch) does that mean I will only have 1 gig transit between the disparate private subnets?

I assume the traffic HAS to pass through the router in order to pass packets to the other private subnets even if is on the same subnet? What is the best practice to achieve maximum local transit is more what I'm asking.