the benefits of segmenting a network is to cut down on broadcasts and traffic going thru the entire network. you can do this with a switch but it has to be a managed switch that is capable of making VLANS. a VLAN basically takes ports that you select on the switch and segments them off from the rest of the network within the switch itself. so if your network is 10.0.1.0 you could segment off 12 ports on a 24 port switch, (or any number of ports you want), and make that network 10.0.2.0, etc. this basically helps manage the network better by breaking down the traffic that is going across the switch. depending on how large the network is and how much traffic is going across it you could be just adding more complexity to the network without any benefits if your network is small.
Carrie Higbie says
There are several benefits to segmenting a network. For one, the router tables in your switches and routers are smaller, (translated take less memory), traffic is forwarded faster as it has less addresses to search through before sending it on to the right device. For broadcasts or traffic that goes to all devices, it is much easier to do with a smaller address pool. You can also set up a network so that one segment may or may not have visibility to another segment which can be an aid in security.
You can do this with switches, provided they have the right software. Some of the lower end switches do not have this feature set. However, layer 3 switches allow this, and switches that let you utilize VLANs will let you do that also.
Security is also another reason to segment a network. This can be done at a physical level with different switches and cabling or can be done at a logical level using encryption like SSL or ipsec.