Prevents accidental connection of switching devices to PortFast-enabled ports. Connecting switches to PortFast-enabled ports can cause Layer 2 loops or topology changes.
Prevents switches connected on ports configured as access ports from becoming the root switch. The core switch, in a simple topology, should be the root.
The Loop Guard STP feature improves the stability of Layer 2 networks by preventing bridging loops.
[Eric Leahy "The World of Networking"](http://ericleahy.com/index.php/bpdu-guard-bpdu-filter-root-guard-loop-guard-udld/#:~:text=BPDU Guard%3A Prevents accidental connection,devices to PortFast-enabled ports.&text=BPDU filtering%3A Restricts the switch,the root switch.)