Based on my studies at Cisco Networking Academy, I know more or less what a router can do. But due to a lack of practical experience, I don't have a clear idea on the following design decision: when is it convenient or necessary to use a router, and when should alternative technologies be used.

For instance, a router can "segment" a network, so that network broadcasts are confined to a smaller number of computers, but at what size of a network (how many computers) does this become relevant? The study text fails to give some sort of rule-of-thumb for this particular question.

I also understand that a router gives access to some additional technologies (like VLAN, for instance), but since many companies here in Bolivia don't use routers, I haven't seen much how they are used in actual practice.

TIA,

Hilmar.