You’re going to have to read this document for yourself. Somehow its possible for an i2002, i2004, i2007, 1120e, 1140e and 1150e to throw a loop into the network when the devices are powered by external power supplies as opposed to using a PoE (Power Over Ethernet) switch.
As a rule of thumb I enable Spanning Tree with Fast Learning on all our edge switches since the auto MDI-X feature makes it very easy for a user or inattentive network engineer to physically put a loop in the connect by connecting to edge ports with the same patch cable.
Update: Thursday December 18, 2008
I’ve fixed the broken link above… Thanks Bob!