Some more notes! From chapter two of Chris Bryant's (@ccie12933) BCMSN study guide and some of my own blending

Why We Create VLANs

The most common reason for creating VLANs: Prevent the excess traffic caused by a switch's default behavior when it receives a broadcast. If you have a network segment with hosts whose very existence should not be known by the rest of the network, just put these hosts into their own VLAN. A switch that receives a broadcast will forward it out every other port on the switch except the one that it was originally received on. A . . . → Read More: SWITCH Study Notes – Virtual LANs (VLANs)