Why turn STP off?!

I have a question for you, why would you want to turn Spanning-Tree Protocol off on Cisco switches?! The Public School system I go to turned off STP for all their catalyst's. I'm very shocked...

They must be absolutely certain that there is no redundant connections. I personally think that this is a bet that is too risky to take. Especially not at a school, where students might decide to bring in a hub, and connect it into two different wall jacks...yeah, it happens.

As for why they may have done this, if they are using old Catalyst switches that don't have PVST or RSTP (they converge very quickly to topology changes as opposed to the original STP time of approximately 30 seconds), so maybe they are trying to eek out a bit more performance.

another reason to disable STP might be to fix the startup delay caused by spanning-tree's blocking, listening, forwarding stages that take time and cause some workstations and servers to fail to connect to the network. Normally this is accomplished with the portfast command, but who knows, maybe they decided it was easier not to run STP instead.

Turning off STP on edge switches will also help them process other frames faster. usually edge switches have only one connection to the next level switch so it is really wastage of the CPU resources to have STP enabled on them. But as already said, one needs to be sure that there is never going to be a physical loop with your network even with new changes. It all depends upon the Network design. Turning off stp will save the CPU cycles and so switch can perform little better.