Broadcast domains and why they still matter
Switching is cheap, so people build large flat networks. Here is what that costs you.
Writing
layer2
Spanning tree: what it protects you from
A layer 2 loop does not degrade a network. It stops it, completely, in seconds.
ARP, and the day two devices claimed one address
Intermittent, symmetrical, affects everyone on the subnet. Duplicate addresses have a signature.